-  Hong Kong University, Oct. 3--9, 1993.
      
  Given talk (1993-10-06):
	A survey of covering theory.
       -  Trento University (Italy), Sept. 24, 1995--Sept. 6, 1996.
       
  Given talk (1995-10-24): A sketch of covering theory.
	>
       -  Genova University (Italy), June 4--6, 1996.
       
  Given talk (1996-06-05):
	 Simple ideas for famous problems.
       -  Pisa University (Italy), July 11--12, 1996.
      
  Given talk (1996-07-11):
      Coverings of the integers and groups.
       -  Center for Combinatorics, Nankai University,
	March 6--August 16, 1999.
      
 -  Hong Kong University of Science and Technology, Feb. 28--April 14, 2000.
      
 -  Chinese University of Hong Kong, April 7, 2000.
       
  Given talk (2000-04-07):
       Various number-theoretic quotients and related congruences.
       -  Hong Kong University, April 10, 2000.
	 
  Given talk (2000-04-10):
       Recent progress on covers of the integers
	  and their applications.
       -  City University of Hong Kong, April 14, 2000.
	  
  Given talk (2000-04-14):
	 On Hilbert's tenth problem and related topics.
       -  Chinese University of Hong Kong, July 23--August 22, 2000.
      
 -  Institute of Mathematics, Academia Sinica (Taiwan), May 1--June 30, 2002.
       
  Given talk (2002-05-16):
	 Equalities and inequalities related to covers of $\Bbb Z$ or groups.
       -  National Sun Yat-sen Univ. (Taiwan), May 27--29, 2002.
       
  Given talk (2002-05-28):
	 On zero-sum problems.
       -  National Taiwan Normal Univ. (Taiwan), June 12, 2002.
       
  Given talk (2002-06-12):
	 On the sum $\sum_{k\equiv r (mod m)}\binom{n}{k}$
	and related results.
       -  National Taiwan Univ., June 24, 2002.
       
  Given talk (2002-06-24):
	 On the structure of periodic arithmetical maps.
       -  National Taiwan Univ., Nov. 4--12, 2002.
       
  Given talk (2002-11-06):
	 On the sum $\sum_{k\equiv r (mod m)}\binom{n}{k}$
	and related results.
       -  Institute of Mathematics, Academia Sinica (Taiwan), Nov. 11, 2002.
       
  Given talk (2002-11-11):
	 Snevily's conjecture on abelian groups and an
	   algebraic method in combinatorics.
       -  Kyushu University (Fukuoka, Japan), Nov. 16--22, 2003.
       
  Given talk (2003-11-21):
	 How to unify covering systems, restricted sumsets and zero-sum
	   problems.
       -  Northwest University (Xi'an, China), Feb. 12--16, 2004.
       
  Given talk (2004-02-13):
	 Recent progress on zero-sum problems and Snevily's conjecture.
       -  ICTP (International Centre for Theoretical Physics) (Trieste, Italy),
	 May 24--June 12, 2004.
      
 -  Graz University (Graz, Austria), June 13--19, 2004.
       
  Given talk (2004-06-14):
	 Covering systems and their connections to zero-sum problems.
       -  Vienna University of Technology (Vienna, Austria), June 17, 2004.
       
  Given talk (2004-06-17):
	 On disjoint systems of residue classes or cosets of subgroups.
        -  Genova University (Genova, Italy), June 20--25, 2004.
       
  Given talk (2004-06-23):
	 On the Erd\"os-Heilbronn conjecture and Snevily's conjecture.
        -  Firenze Univ. (Florence, Italy), June 26--28, 2004.
       
  Given talk (2004-06-28):
	 On various combinatorial sums and related identites.
        -  Univ. Roma "Tor Vergata" (Rome, Italy), June 28--30, 2004.
       
  Given talk (2004-06-30):
	 Two local-global theorems and a powerful formula.
        -  Institut Camille Jordan, Universit\'e
	Claude Bernard Lyon-I (France), Jan. 11--March 10, 2005.
       
  A typical talk (2005-01-13):
	 Identities and congruences for Bernoulli and Euler polynomials.
        -  Univ. Saint-Etienne (France), Feb. 1, 2005.
       
  Given talk (2005-02-01):
	 Problems and results on covering systems.
        -  Univ. Bordeaux I (France), Feb. 16--18, 2005.
       
  Given talk (2005-02-17):
	 Some effective results related to covers of Z and zero-sum problems.
        -  Univ. California at Irvine (USA), May 13, 2005--May 6, 2006.
       
  Given talk (2005-05-25):
         Problems and results on covering systems.
         Given talk (2005-11-10):
         On some conjectures of Erdos-Heilbronn, Lev and Snevily.
         Given talk (2006-01-19):
         A survey of zero-sum problems on abelian groups.
        -  Univ. Wisconsin at Madison (USA), April 3--8, 2006.
       
  Given talk (2006-04-04):
         Some curious results on Bernoulli and Euler polynomials
         Given talk (2006-04-06):
         Recent progress on congruences involving binomial coefficients.
        -  Univ. Illinois at Urbana-Champaign (USA), April 12--14, 2006.
       
  Given talk (2006-04-13):
         Covering systems and periodic arithmetical functions.
        -  Massachusetts Institute of Technology (MIT, USA), April 20--22, 2006.
       
  Given talk (2006-04-21):
         Combinatorial aspects of covers of groups by cosets or subgroups.
        -  Zhejiang Univ., May 24--28, 2006.
       
  Given talk (2006-05-26):
	 Some congruences motivated by algebraic topology.
        -  ECNU Workshop on q-Series (East-China Normal Univ., June 21, 2006).
       
  Given talk (2006-06-21):
	 Some congruences concerning q-Euler numbers,
	q-Salie numbers and q-Carlitz numbers.
        -  Internat. Workshop on Finite Fields and their Appl. (Chenxing Math. Center, July 3--7, 2006).
       
  Given talk (2006-07-07):
	 p-adic orders of some sums involving binomial coefficients.
        -  The Fourth China-Japan Conf. on Number Theory (Shandong Univ., Weihai, Aug. 30--Sept. 3, 2006).
	
  Given talk (2006-08-30):
	 Curious identities and congruences involving Bernoulli polynomials.
	 -  Beijing Normal University, Jan. 25, 2007.
       
  Given talk (2007-01-25):
	 Problems and results on restricted sumsets.
        -  The Institute of Mathematics, Chinese Academy of Sciences (Beijing), Jan. 22--30, 2007.
	
  Given talk (2007-01-30):
	 Combinatorial aspects of Szemeredi's theorem.
        -  Zhejiang University, April 5--8, 2007.
       
  Given talk (2007-04-06):
	 Additive combinatorics and Latin transversals.
        -  The Fourth Cross-Strait Conf. on Graph Theory and Combin.
	(National Taiwan Univ., Taipei, June 24--27, 2007).
	
  Given talk (2007-06-24):
	 An additive theorem and restricted sumsets.
	 -  National Cheng Kung University (Tainan), June 28--29, 2007.
       
  Given talk (2007-06-28):
	 Sums of squares and triangular numbers, and Rado numbers for linear equations.
        -  The 19th Annual Int. Conf. on Formal Power Series and Algebraic Combin.
	 (Nankai Univ., Tianjin, July 2--6, 2007).
	
  Given talk (2007-07-04):
	 An additive theorem related to Latin transversals.
        -  The 2007 Annual. Conference of the Chinese Math. Soc.
	   (Beijing,  Nov. 1--4, 2007).
       
  Invited talk (2007-11-3):
	 Some famous problems and related results in combinatorial number theory.
        -  The 4th Int. Congress of the Chinese Mathematicians
	 (Zhejiang  Univ., Hangzhou, Dec. 17--22, 2007).
	
  Invited talk (2007-12-21):
	 Groups in combinatorial number theory.
        -  Tongji Univ., Shanghai, Jan. 18--21, 2007.
	
  Given talk (2008-01-18):
	 Various extensions of some basic results in combinatorial number theory.
        -  The 6th Shanghai Conference on Combinatorics
	 (Shanghai Jiao Tong Univ., May 24--28, 2008).
	
  Plenary talk (2008-05-28):
	 Recent problems and results involving binomial coefficients.
        -  Suzhou Univ., Suzhou, June 18--20, 2008.
	
  Given talk (2008-06-19):
	 An extremal problem on covers of abelian groups.
	 -  Nankai Univ., Tianjin, June 23--25, 2008.
	
  Given talk (2008-06-24):
	 An extremal problem on covers of abelian groups.
	  -  The Institute of Mathematics, Chinese Academy of Sciences (Beijing), June 26--30, 2008.
	
  Given talk (2007-06-29):
	 Study covers of groups via characters and number theory.
	  -  The 5th China-Japan Conf. on Number Theory (Kinki Univ., Osaka, Japan), August 27--Sept.1, 2008.
	
  Given talk (2008-08-28):
	 On representations of integers involving triangular numbers.
	 -  Dalian University of Technology, Dalian, Nov. 29--Dec. 3, 2008.
	
  Given talk (2008-12-01):
	 An extremal problem on covers of abelian groups.
	 -  Anhui Normal University, Wuhu, April 22--25, 2009.
	
  Given talk (2009-04-23):
	 Some new conjectures involving primes.
	 -  Ynacheng Normal College, Yancheng, Jiangsu Province, June 14--17, 2009.
	
  Given talk (2009-06-16):
	 Some new conjectures involving primes.
	 -  The Fifth Cross-Strait Conf. on Graph Theory and Combin.
	(Nankai Univ., Tianjin, July 28--August 1, 2009).
	
  Plenary (one-hour) talk  (2009-07-31):
	 Probelms and results in additive combinatorics.
	 -  International Conference on Number Theory and Representations
	(Shandong Univ., Weihai, August 2--August 7, 2009).
	
  Given talk	(2009-08-03):
	 Polygonal numbers, primes and ternary quadratic forms.
	 -  Harish-Chandra Research Institute (Jhusi, Allahabad, India), Jan. 16--Feb. 16, 2010.
	
  Six talks were given, here are the last three:  
	 (Feb. 4, 2010)
	 On the DKSS technique and the DKSS conjecture. 
	 (Feb. 6, 2010)
	 Some sophisticated applications of the Combinatorial Nullstellensatz. 
	 (Feb. 8, 2010)
	 Conjectures and results on super congruences. 
	 -  Capital Normal University, Beijing, April 8--10, 2010.
	
  Given talk (2010-04-09):
	 Conjectures for super congruences and series for
	 π and other constants.
	 -  The Second International Workshop on Number Theory, Combinatorics and their Interactions
	(Luoyang Normal Univ., Luoyang, May 1--3, 2010).
	
  Given talk	(2010-05-02):
	 Conjectures for super congruences and series for
	 π and other constants.
	 -  Pacific Rim Conference on Mathematics
	(Stanford University (USA), June 28--July 2, 2010).
	
  Invited talk	(2010-07-02):
	 Super congruences involving binomial coefficients and new series for
	 some famous constants.
	 -  The National Center for Theoretical Sciences
	(Hsinchu, Taiwan; August 1--August 8, 2010).
	
  Given talk	(2010-08-02):
	 Problems and results in additive combinatorics.
	  Given talk	(2010-08-04):
	 Arithmetic properties of combinatorial quantities.
	 -  The National Chiao Tung University
	(Hsinchu, Taiwan; August 5, 2010).
	
  Given talk	(2010-08-05):
	 On divisibilitity concerning binomial coefficients.
	 -  The 5th National Conference on Number Theory
	(Zhaoqing, Guangdong, China; December 25-28, 2010).
	
  Given talk	(2010-12-27):
	 Correspondence between series and congruences.
	 -  Shanghai Jiaotong University (March 14-18, 2011).
	
  Given talk (2011-03-15):
	 p-adic congruences on combinatorial sums involving binomial coefficients,
	  Given talk (2011-03-17):
	 p-adic congruences on combinatorial sums involving binomial coefficients (II). 
	 -  Zhejiang University
	(Hangzhou, China; March 24-26, 2011)
	
  Given talks (2011-03-25):  
	 (1) On weighted extension of the Erdos-Heilbronn conjecture, 
	 (2) Dense subsets of the ring of p-adic integers and combinatorial congruences.
	 -  Hsinghua University
	(Beijing, China; April 13-14, 2011).
	
  Given talk	(2011-04-14):
	 Number theory behind series for 1/π.
	 -  Institute of Mathematics, Chinese Academy of Sciences
	(Beijing, China; April 15, 2010)
	
  Given talk	(2011-04-15):
	 On the DKSS conjecture for finite abelian groups.
	 -  Capital Normal University
	(Beijing, China; April 15, 2011)
	
  Given talk	(2011-04-15):
	 Determining
      x2 mod
      p2 with
      4p=x2+dy2.
	 -  Workshop in Combinatorics (Peking University, China; May 7-8, 2011)
	
  Given talk	(2011-05-7):
	 On the DKSS conjecture for finite abelian groups.
	 -  Chern Institute of Mathematics, Nankai University
	(Tianjin, China; May 9-15, 2011)
	
  Given talk	(2011-05-11):
	 Number theory behind series for 1/π.
	 -  Shandong University
	(Jinan, China; May 24-26, 2010)
	
  Given talk	(2010-05-25):
	 On the DKSS conjecture for finite abelian groups.
	 -  Conference on Number Theory and relatd Fields
	(Hefei and Huangshan, China; June 7-12, 2011)
	
  Given talk	(2010-06-08):
	 Conjectures and results on
      x2 mod
      p2 with
      4p=x2+dy2.
         -  The National Chiao Tung University
         (Hsinchu, Taiwan; June 27-July 2, 2011)
        
  Given talk (2010-06-28):
         Combinatorial congruences via the Zeilberger algorithm.
       -  Institute of Mathematics, Academia Sinica (Taiwan), July 3-24, 2011.
       
  Given talk (2011-07-06):
         On arithmetic properties of Bell numbers and Delannoy numbers.
         Given talk (2011-07-12):
         Conjectures and results on generalized central trinomial
         coefficients and Motzkin numbers.
         Given talk (2011-07-14):
         Number theory behind series for 1/π.
         -  I-Shou University
         (Kaohsiung, July 18-19, 2011)
        
  Given talk (2011-07-19):
         On the DKSS conjecture for finite abelian groups.
	 -  The National Center for Theoretical Sciences
        (Hsinchu, Taiwan; July 19-22, 2011).
        
  Given talk (2011-07-20):
         Some sophisticated congruences involving Fibonacci numbers.
         -  East-China Normal University (Shanghai; Oct. 27-29, 2011).
        
  Given talk (2011-10-29):
         Number Theory behind Series for Powers of π.
         -  The 2nd National Conference on Combinatorial Number Theory (Guangzhou; Nov. 24-26, 2011).
        
  Given talk (2011-11-25):
         p-adic Congruences Motivated by Series.
         -  Jiangsu Normal University (Xuzhou; March 22, 2012).
        
  Given talk (2012-03-22):
         On Functions Taking Only Prime Values.
         -  The Morningside Center of Mathematics (Beijing), April 18--22, 2012.
	
  Given talk (2012-04-21):
	 On Functions Taking Only Prime Values and Related New Conjectures on Primes.
         -  Tsinghua University (Beijing), April 20, 2012.
	
  Given talk (2012-04-20):
	 Some Sophisticated Congruences involving Fibonacci Numbers.
         -  Workshop on Combinatorics and Graph Theory (Changsha; June 9-11, 2011).
        
  Plenary talk (2012-06-10):
         Generate Primes in a Combinatorial Manner.
          -  The 5th National Conference on Combinatorics and Graph Theory (Luoyang; July 16-19, 2011).
        
  Plenary talk (2012-07-18):
         Primes from the Viewpoint of Combinatorics.
         -  University of Illinois at Urbana-Champaign, USA (July 23-August 30, 2012).
        
  Given talk (2012-08-28):
         Various New Observations about Primes.
         -  City University of New York, USA (August 23-24, 2012).
        
  Given talk (2012-08-23):
         p-adic Congruences Motivated by Series.
         -  Dalian University of Technology (Nov. 14-15, 2012).
        
  Given talk (2012-11-15):
         Refinements of Some Famous Problems on Primes.
         -  Dalian Maritime University (Nov. 16-17, 2012).
        
  Given talk (2012-11-16):
         Conjectures involving Arithmetical Sequences.
         -  Center for Combinatorics, Nankai University (Nov. 30--Dec. 2, 2012).
        
  Given talk (2012-12-01):
         The Riddle of Primes.
         -  Tsinghua University (April 12, 2013).
        
  Given talk (2013-04-12):  Apery Numbers, Franel Numbers and Binary Quadratic Forms.
         -  The Morningside Center of Mathematics (Beijing), April 13--15, 2013.
	
  Given talk (2013-04-13):
	 Sums of Consecutive Primes and Related Conjectures.
         -  Hong Kong University of Science and Technology (April 26--May 5, 2013).
        
  Given talk (2013-05-02):  Apery Numbers, Franel Numbers and Binary Quadratic Forms.
         -  Hong Kong University (May 3, 2013).
	
  Given talk (2013-05-03):
	 Some New Representation Problems involving Primes.
         -  Guangxi Normal University (June 22-26, 2013).
        
  Given talk (2013-06-24):
         Combinatorial Congruences via Zeilberger's Algorithm and Trees with Prime Vertices.
         -  The 5th International Symposium on Graph Theory and Combin. Algorithms (July 12-15, 2012).
        
  Given talk (2012-07-14):
         Combinatorial Congruences via Zeilberger's Algorithm and Trees with Prime Vertices.
         -  Zhejiang Univ. (Nov. 14-17, 2013).
        
  Given talk (2013-11-15):
         Determinants, Permutations and Additive Combinatorics.
         -  Xiamen Univ. (Dec. 19-22, 2013).
        
  Given talk (2013-12-20):
         Write n = k+m with f(k,m) Prime.
         -  Central China Normal Uni. (Jan. 2-5, 2014).
        
  Given talk (2014-01-03):
         Congruences for Franel Numbers.
         -  Xiamen Univ. (March 20-23, 2014).
        
  Given talk (2014-03-21):
         Problems on Combinatorial Properties of Primes.
         -  Tsinghua Univ. (April 18, 2014).
        
  Given talk (2014-04-18):
         Problems on Combinatorial Properties of Primes.
         -  The Morningside Center of Mathematics (Beijing), April 16--20, 2014.
        
  Given talk (2014-04-19):
         Determinants, Permutations and Additive Combinatorics.
         -  The 2nd Workshop on Combinatorics and Graph Theory (Changsha, June 1-2), 2014.
        
  Given talk (2014-06-02):
         Determinants, Permutations and Additive Combinatorics.
         -  The Workshop on Analytic Number Theory and Cryptology (Beijing, June 14-15), 2014.
        
  Given talk (2014-06-14):
         On Some Arithmetic Functions.
         -  Institute of Mathematics, Academia Sinica (Taiwan), July 15--29, 2014.
        
  Given talk (2014-07-24):
         Determinants, Permutations and Additive Combinatorics.
         -  Impact of Computation on Number Theory (National Center of Theoretical Science, Hsinchu, July 30--August 3), 2014.
        
  Plenary talk (2014-08-03):
         Determinants, Permutations and Additive Combinatorics.
         -  National Center of Theoretical Science, Hsinchu, Taiwan, July 29--August 10, 2014.
        
  Given talk (2014-08-06):
         Towards the Twin Prime Conjecture.
         -  Northwest University, Xi'an, October 25--28, 2014.
        
  Given talk (2014-10-26):
         Towards the Twin Prime Conjecture.
          Given talk (2014-10-27):
         Supercongruences Motivated by e.
         -  Center for Applied Mathematics, Tianjin Univ., Oct. 30--Nov. 2, 2014.
        
  Given talk (2014-10-31):
         Congruences for Franel Numbers.
         -  Center for Combinatorics, Nankai Univ., Tianjin, Nov. 3-4, 2014.
        
  Given talk (2014-11-03):
         Towards the Twin Prime Conjecture.
         -  Jiangsu Normal Univ., Xuzhou, Jan. 8-11, 2015.
        
  Given talk (2015-01-09):
         On generalized central trinomial coefficients.
         -  Capital Normal Univ., Beijing, April 19-21, 2015.
        
  Given talk (2015-04-20):
         On combinatorial properties of primes.
         -  Tsinghua Univ., Beijing, May 8, 2015.
        
  Given talk (2015-05-08):
         On universal sums involving polygonal numbers.
         -  The Morningside Center of Mathematics (Beijing), May 7--11, 2015.
        
  Given talk (2015-05-10):
         Consecutive primes and Legendre symbols.
         -  Dalian University of Technology, May 28--31, 2015.
        
  Given talk (2015-05-29):
         On generalized central trinomial coefficients.
         -  Connections in Discrete Mathematics (Simon Fraser Univ., Burnaby, Vancouver, Canada, June 15--19, 2015).
        
  Given talk (2015-06-16):
         On universal sums involving polygonal numbers.
         -   The 8th Cross-Strait Conf. on Graph Theory and Comb.(National Sun Yat-sen Univ., Kaohsiung, June 26--July 2, 2015).
        
  Given talk (2015-06-28):
         New divisibility results on certain sums of binomial coefficients.
         -  Suzhou University, January 10--12, 2017.
        
  Given talk (2017-01-11):
         The 1-3-5 conjecture and related topics.
         -  Jiangsu Normal University, March 11--14, 2017.
        
  Given talk (2017-03-13):
         Restricted sums of three or four squares.
         -  Institute of Mathematics, Chinese Academy of Sciences, April 15--18, 2017.
        
  Given talk (2017-04-18):
         Further results on Hilbert's tenth problem.
         -  Institute of Mathematics, Chinese Academy of Sciences, April 21--24, 2017.
        
  Given talk (2017-04-22):
         On three-square theorem and its applications.
         -  Hebei Normal University, May 13--16, 2017.
        
  Given talk (2017-05-15):
         On Hilbert's tenth problem.
          -  The 5th National Conf. on Combin. Number Theory (Huaiyin Normal College, Sept. 15--17, 2017).
        
  Given talk (2017-09-16):
         On Hilbert's tenth problem.
         -  Northwest University, October 18--21, 2017.
        
  Given talk (2017-10-19):
         On the DKSS conjecture for finite abelian groups.
          Given talk (2017-10-20):
         On the generalized central trinomial coefficients.
         -  The 9th Cross-strait Conf. on Graph Theory and Combin., November 2--5, 2017.
        
  Plenary talk (2017-11-3):
         A survey of arithmetic properties of combinatorial quantities.
         -  Jiangsu  University, November 23--26, 2017.
        
  Given talk (2017-11-24):
         On Snevily's conjecture and related topics.
         -  Shandong  University, November 30--December 3, 2017.
        
  Given talk (2017-12-01):
         On Snevily's conjecture and related topics.
         -  The 3rd Workshop on Combinatorics and Graph Theory at Hunan University (Changsha, December 8--10, 2017).
        
  Given talk (2017-12-10):
         On Snevily's conjecture and related topics.
         -  The 4th Sichuan-Chongqing Workshop on Number Theory (Nanchong, December 22--24, 2017).
        
  Given talk (2017-12-23):
         On universal sums x(ax+b)/2+y(cy+d)/2+z(ez+f)/2.
         -  Southern Univ. of Sci. and Tech., Janunary 11--13, 2018.
        
  Given talk (2018-01-12):
         On covers of groups by cosets.
         -  Shenzhen Univ., January 13, 2018.
        
  Given talk (2018-01-13):
         On universal sums x(ax+b)/2+y(cy+d)/2+z(ez+f)/2.
         -  Xia Univ., Jaunary 14--16, 2018.
        
  Given talk (2018-01-15):
         On Hilbert's tenth problem.
         -  Xia Univ., Jaunary 14--16, 2018.
        
  Given talk (2018-01-15):
         On Hilbert's tenth problem.
         -  Institute of Systems Science, Chinese Academy of Sciences, January 28-30, 2018.
        
  Given talk (2018-01-29):
         Problems and results on sums of squares.
         -  Conference on Combinatorics and its Applications (Harbin, May 18-20, 2018).
        
  Given talk (2018-05-19):
         Determinants, permutations and additive combinatorics.
         -  Wuhan Univ., June 14-17, 2018.
        
  Given talk (2018-06-15):
         Problems and results on sums of squares.
         -  Saint Petersburg Dept. of Steklov Math. Institute of Russian Academy of Sciencess (July 15-30, 2018).
        
  Given talk (2018-07-19):
         Determinants, permutations and additive combinatorics.
          Given talk (2018-07-20):
         Problems and results on sums of squares.
         -  Summer Research Institute on q-Series (Tianjin, July 25--August 15, 2018).
        
  Given talk (2018-08-14):
         Historical remarks on my conjectural series.
          Given talk (2018-08-15):
         On q-analogues of some identities and congruences.
         -  2018 Conference on Number Theory and its Applications (Yan'an, August 19-22, 2018).
        
  Given talk (2018-08-20):
         On some determinants involving Legendre or Jacobi symbols.
	 
	 
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