Moa Apagodu

Using the “Freshman's Dream” to Prove Combinatorial Congruences

Abstract Recently, William Y.C. Chen, Qing-Hu Hou, and Doron Zeilberger developed an algorithm for finding and proving congruence identities (modulo primes) of indefinite sums of many combinatorial sequences, namely those (like the Catalan and Motzkin sequences) that are expressible in terms of constant terms of powers of Laurent polynomials. We first give a leisurely exposition of their approach and then extend it in two directions. The Laurent polynomials may be of several variables, and instead of single sums we have multiple sums. In fact, we even combine these two generalizations. We conclude with some super-challenges.

Elementary proof of congruences involving sum of binomial coefficients

We provide elementary proof of several congruences involving single sum and multisums of binomial coefficients.