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 A151346 #15 Mar 13 2019 11:54:18
%S A151346 1,0,1,1,2,7,10,38,89,229,752,1873,6009,17746,51970,168199,503489,
%T A151346 1609327,5131184,16183314,53017947,170708648,559207257,1846295302,
%U A151346 6075728984,20284263554,67649481468,226890912838,765669449228,2585600921015,8785174853897,29918390234278,102190450691351,350429638975797
%N A151346 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, 0)}.
%H A151346 Alois P. Heinz, <a href="/A151346/b151346.txt">Table of n, a(n) for n = 0..1000</a>
%H A151346 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 8, Tag 9.
%H A151346 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 A151346 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, 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}]
%Y A151346 Column k=0 of A199915 and of A306814.
%K A151346 nonn,walk
%O A151346 0,5
%A A151346 _Manuel Kauers_, Nov 18 2008