This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A133413 #7 Jan 07 2023 19:01:41
%S A133413 1,2,24,492,202064,100202536,888531141152,8548846756027594,
%T A133413 1400822035743239844640,241149984205773848119833656,
%U A133413 691305758149247080625180837349904,2048332087899166877612856148780183708362,99840603982108483679316058344233421388081447648
%N A133413 Half the number of ways of placing up to n^2 pawns on an n x n chessboard so that it balances at its midpoint.
%o A133413 (PARI) a(n) = {polcoef(polcoef(prod(j=1, n, prod(k=1, n, 1 + 'x^(2*k-n-1)*'y^(2*j-n-1) )), 0), 0)/2} \\ _Andrew Howroyd_, Jan 07 2023
%Y A133413 Cf. A133406, A133414.
%K A133413 nonn
%O A133413 1,2
%A A133413 _R. H. Hardin_, Nov 25 2007
%E A133413 a(12)-a(13) from _Andrew Howroyd_, Jan 07 2023