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 A151335 #11 Dec 27 2023 01:20:42
%S A151335 1,0,0,1,0,1,5,1,18,43,47,313,570,1480,5847,11715,41194,124918,317707,
%T A151335 1120909,3159179,9581991,31624946,92407981,300936377,954921610,
%U A151335 2965630143,9769316877,30986916602,100406899586,329864837841,1066298792633,3525879988702,11612179660287,38300799541992,127788972039783
%N A151335 Number of walks within N^2 (the first quadrant of Z^2) starting and ending at (0,0) and consisting of n steps taken from {(-1, 0), (-1, 1), (0, 1), (1, -1)}.
%H A151335 Alois P. Heinz, <a href="/A151335/b151335.txt">Table of n, a(n) for n = 0..1000</a>
%H A151335 A. Bostan, K. Raschel, B. Salvy, <a href="http://dx.doi.org/10.1016/j.jcta.2013.09.005">Non-D-finite excursions in the quarter plane</a>, J. Comb. Theory A 121 (2014) 45-63, Table 1 Tag 12
%H A151335 M. Bousquet-Mélou and M. Mishna, 2008. Walks with small steps in the quarter plane, <a href="http://arxiv.org/abs/0810.4387">ArXiv 0810.4387</a>.
%t A151335 aux[i_Integer, j_Integer, n_Integer] := Which[Min[i, j, n] < 0 || Max[i, j] > n, 0, n == 0, KroneckerDelta[i, j, n], True, aux[i, j, n] = aux[-1 + i, 1 + j, -1 + n] + aux[i, -1 + j, -1 + n] + aux[1 + i, -1 + j, -1 + n] + aux[1 + i, j, -1 + n]]; Table[aux[0, 0, n], {n, 0, 25}]
%K A151335 nonn,walk
%O A151335 0,7
%A A151335 _Manuel Kauers_, Nov 18 2008