We study the generating functions for pattern-restricted $k$-ary words of length $n$ corresponding to the longest alternating subsequence statistic in which the pattern is any one of the six permutations of length three.

We extend an argument of Felix Behrend to show that fairly dense subsets of the integers exist which contain no solution to certain systems of linear equations.

Using combinatorial methods, we derive several formulas for the volume of convex bodies obtained by intersecting a unit hypercube with a halfspace, or with a hyperplane of codimension 1, or with a flat defined by two parallel hyperplanes. We also describe some of the history of these problems, dating to Polya’s Ph.D. thesis, and we discuss several applications of these formulas.

Let ${\mathbb{F}}_2^n$ be the finite field of cardinality $2^n$. For all large $n$, any subset $A\subset {\mathbb{F}}_2^n\times {\mathbb{F}}_2^n$ of cardinality
$$|A|\gtrsim \frac{4^n\log \log n}{\log n},$$
must contain three points $\{(x,y),(x+d,y),(x,y+d)\}$ for $x,y,d\in {\mathbb{F}}_2^n$ and $d\ne 0$. Our argument is an elaboration of an argument of Shkredov [14], building upon the finite field analog of Ben Green [10]. The interest in our result is in the exponent on $\log n$, which is larger than has been obtained previously.

In 1972, Bender and Knuth established a bijection between certain infinite matrices of non-negative integers and plane partitions and in [2] a bijection between Bender-Knuth matrices and n-color partitions was shown. Here we use this later bijection and translate the recently found n-color partition theoretic interpretations of four mock theta functions of S. Ramanujan in [1] to new combinatorial interpretations of the same mock theta functions involving Bender-Knuth matrices.

We present analytical properties of a sequence of integers related to the evaluation of a rational integral. We also discuss an algorithm for the evaluation of the 2-adic valuation of these integers that has a combinatorial interpretation.

It is proposed that finding the recursion relation and generating function for the (colored) Motzkin numbers of higher rank introduced recently is an interesting problem.

Let ${\mathbb{F}}_2^n$ be the finite field of cardinality $2^n$. For all large $n$, any subset $A\subset {\mathbb{F}}_2^n\times {\mathbb{F}}_2^n$ of cardinality $$|A|\gtrsim \frac{4^n\log \log n}{\log n},$$ must contain three points $\{(x,y),(x+d,y),(x,y+d)\}$ for $x,y,d\in {\mathbb{F}}_2^n$ and $d\ne 0$. Our argument is an elaboration of an argument of Shkredov [14], building upon the finite field analog of Ben Green [10]. The interest in our result is in the exponent on $\log n$, which is larger than has been obtained previously.