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 A147999 #4 Dec 28 2023 20:13:23
%S A147999 1,1,2,3,8,15,39,77,244,543,1655,3729,12385,29510,93170,221283,764948,
%T A147999 1908675,6323115,15688889,55069789,141067986,473165330,1200395415,
%U A147999 4290381497,11232104990,38585190644,100082744787,360316046969,956558534943,3305432502421,8679121868177,31575545872868,84905308145331
%N A147999 Number of walks within N^3 (the first octant of Z^3) starting at (0,0,0) and consisting of n steps taken from {(-1, -1, -1), (-1, -1, 1), (-1, 1, 0), (1, 0, 0)}.
%H A147999 A. Bostan and M. Kauers, 2008. Automatic Classification of Restricted Lattice Walks, <a href="http://arxiv.org/abs/0811.2899">ArXiv 0811.2899</a>.
%t A147999 aux[i_Integer, j_Integer, k_Integer, n_Integer] := Which[Min[i, j, k, n] < 0 || Max[i, j, k] > n, 0, n == 0, KroneckerDelta[i, j, k, n], True, aux[i, j, k, n] = aux[-1 + i, j, k, -1 + n] + aux[1 + i, -1 + j, k, -1 + n] + aux[1 + i, 1 + j, -1 + k, -1 + n] + aux[1 + i, 1 + j, 1 + k, -1 + n]]; Table[Sum[aux[i, j, k, n], {i, 0, n}, {j, 0, n}, {k, 0, n}], {n, 0, 10}]
%K A147999 nonn,walk
%O A147999 0,3
%A A147999 _Manuel Kauers_, Nov 18 2008