%N a(n) = least m such that there is a component of a certain pawn game based on a word of length m that is equivalent to a Nim-heap of size n.
%D Noam D. Elkies, Higher Nimbers in pawn endgames on large chessboards, pages 61-78 in More Games of No Chance, R. J. Nowakowski, ed.; MSRI Publ. #42, 2002 via Cambridge Univ. Press; Proceedings of the 7/00 MSRI Workshop on Combinatorial Games. See Section 6.3.
%H Noam D. Elkies, <a href="https://arxiv.org/abs/math/0011253">Higher Nimbers in pawn endgames on large chessboards</a>, arXiv:math/0011253 [math.CO], 2000. See Section 6.3.
%A _N. J. A. Sloane_, Feb 28 2020