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Moa Apagodu

Publications and source records attributed to Moa Apagodu.

11 recordsLinked to original sources
arXiv2018

Zeilberger to the rescue

We provide both human and computer (even better collaboration between the two) proofs to four recent American Mathematical Monthly problems, namely problem 11897, problem 11899, problem 11916, and problem 11928. We also show that problem 11928 may lead to interesting combinatorial identities.

math.NT↗
arXiv2017

Analysis of the gift exchange problem

In the gift exchange game there are n players and n wrapped gifts. When a player's number is called, that person can either choose one of the remaining wrapped gifts, or can "steal" a gift from someone who has already unwrapped it, subject to the restriction that no gift can be stolen more than a total of sigma times. The problem is to determine the number of ways that the game can be played out, for given values of sigma and n. Formulas and asymptotic expansions are given for these numbers. This work was inspired in part by a 2005 remark by Robert A. Proctor in the On-Line Encyclopedia of Integer Sequences.

math.CO↗
arXiv2016

Using the "Freshman's Dream" to Prove Combinatorial Congruences

In a recent beautiful but technical article, 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 elementary but brilliant 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. In this version we report that Roberto Tauraso pointed out that all our conjectured super-congruences, at the end of our article are already known, except one, for which he supplied a beautiful proof that can be found here: arXiv:1606.05543.

math.CO↗
arXiv2015

Wilf's "Snake Oil" Method Proves an Identity in The Motzkin Triangle

We give yet-another illustration of using Herb Wilf's Snake Oil Method, by proving a certain identity between the entries of the so-called Motzkin Triangle, that arose in a recent study of enumeration of certain classes of integer partitions. We also briefly illustrate how this method can be applied to general `triangles'.

math.CO↗
arXiv2009

Some Nice Sums are Almost as Nice if you turn them Upside Down

We represent the sums $\sum_{k=0}^{n-1}{n \choose k}^{-2}$, $\sum_{k=0}^m{m\choose k}^{-1}{a\choose n-k}^{-1}$, $\sum_{k=0}^{n-1}\frac{q^{-k(k-1)}}{{\genfrac{[}{]}{0pt}{}{n}{k}}_q}$, and the sum of the reciprocals of the summands in Dixon's identity, each as a product of an {\it indefinite hypergeometric sum} times a (closed form) {\it hypergeometric sequence}

math.CO↗