Accurate Bounds for New Van Der Waerden Type Numbers

Bruce M. Landman1, Raymond N. Greenwell2
1Department of Mathematics University of North Carolina at Greensboro Greensboro, NC 27412
2Department of Mathematics Hofstra University Hempstead, NY 11550 USS.A.

Abstract

Numbers similar to those of van der Waerden are examined by considering sequences of positive integers \(\{x_1, x_2, \ldots, x_n\}\) with \(x_{i+1} = x_i + d + r_i\), where \(d \in {Z}^+\) and \(0 \leq r_i \leq \max(0, f(i))\) for a given function \(f\) defined on \({Z}^+\). Let \(w_f(n)\) denote the least positive integer such that if \(\{1, 2, \ldots, w_f(n)\}\) is \(2\)-colored, then there exists a monochromatic sequence of the type just described. Tables are given of \(w_f(n)\) where \(f(i) = i – k\) for various constants \(k\), and also where \(f(i) = i\) if \(i \geq 2\), \(f(1) = 0\). In this latter case, as well as for \(f(i) = i \), an upper bound is given that is very close to the actual values. A tight lower bound and fairly reasonable upper bound are given in the case \(f(i) = i – 1\).