The number of N-point digital discs

Abstract

A digital disc is the set of all integer points inside some given disc. Let DN be the number of different digital discs consisting of N points (different up to translation). The upper bound D N = O(N2) was shown recently; no corresponding lower bound is known. In this paper, we refine the upper bound to DN = O(N), which seems to be the true order of magnitude, and we show that the average DN = D1 + D2 + ... + DN)/N has upper and lower bounds which are of polynomial growth in N.