arXiv subjects
Publications and source records attributed to Thotsaporn "Aek" Thanatipanonda.
We present a short "proof from the Book" that $321$-avoiding permutations without double deficiencies are counted by the Motzkin numbers. Although this result was first proved by Rubey and Stump, our proof gives a much simpler and more transparent description of the same bijection.
In the spirit of "multi-culturalism", we use four kinds of computations: simulation, numeric, symbolic, and "conceptual" to explore some "games of pure chance" inspired by children board games like "Snakes and Ladders" (aka as "Chutes and Ladders") and "gambler's ruin with unlimited credit". Even more interesting than the many computer-generated actual results described in this paper and its web-site extension, is our broad-minded, ecunemical approach, not favoring, a priori, any one of the above four kinds of computation, but showing that, a posteriori, symbolic computation is the most important one, since (except for simulation, that is very inaccurate) numerics can be made more efficient with the help of symbolics (in the "downward" direction), and, (in the "upward" direction) the mere existence of certain symbolic-computational algorithms imply interesting "qualitative" results, that certain numbers are always rational, or always algebraic, and certain sequences are always polynomial, or C-recursive, or algebraic, or holonomic. This article is accompanied by four Maple packages, and numerous input and output files, that readers can use as templates for their own investigations.
We discuss a problem posed by Ronald Graham about the minimum number, over all 2-colorings of $[1,n]$, of monochromatic $\{x,y,x+ay\}$ triples for $a \geq 1$. We give a new proof of the original case of $a=1$. We show that the minimum number of such triples is at most $\frac{n^2}{2a(a^2+2a+3)} + O(n)$ when $a \geq 2$. We also find a new upper bound for the minimum number, over all $r$-colorings of $[1,n]$, of monochromatic Schur triples, for $r \geq 3$.
We prove three conjectures concerning the evaluation of determinants, which are related to the counting of plane partitions and rhombus tilings. One of them was posed by George Andrews in 1980, the other two were by Guoce Xin and Christian Krattenthaler. Our proofs employ computer algebra methods, namely, the holonomic ansatz proposed by Doron Zeilberger and variations thereof. These variations make Zeilberger's original approach even more powerful and allow for addressing a wider variety of determinants. Finally, we present, as a challenge problem, a conjecture about a closed-form evaluation of Andrews's determinant.
For any integer $r \geq 1$, the sequence of numbers $\{{c^{(r)}_{k}}\}_{k \geq 0} $ is defined implicitly by [\sum_k\binom{n}{k}^r\binom{n+k}{k}^r = \sum_k\binom{n}{k}\binom{n+k}{k}c^{(r)}_k,\quad n=0,1,2,...] Asmus Schmidt conjectured that all $c^{(r)}_k$ are integers. We give a new proof of this fact.