%I A151284
%S A151284 1,2,6,20,70,254,942,3550,13532,52030,201386,783560,3061442,12001804,47181278,
               185904220,
%T A151284 733908634,2901998092,11490757796,45552262860,180762964146,717939220774,
               2853611232902,
%U A151284 11349816190552,45168339253888,179845805435900,716409551285034,2854926106932244
%N A151284 Number of walks within N^2 (the first quadrant of Z^2) starting at (0,
               0) and consisting of n steps taken from {(-1, 1), (0, 1), (1, -1), 
               (1, 0)}
%H A151284 M. Bouquet-Melou and M. Mishna, 2008. Walks with small steps in the quarter 
               plane, <a href="http://arxiv.org/abs/0810.4387">ArXiv 0810.4387</
               a>.
%H A151284 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 A151284 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[-1 + i, 1 + j, -1 + n] + aux[i, -1 + 
               j, -1 + n] + aux[1 + i, -1 + j, -1 + n]]; Table[Sum[aux[i, j, n], 
               {i, 0, n}, {j, 0, n}], {n, 0, 25}]
%Y A151284 Sequence in context: A000984 A087433 A119373 this_sequence A049138 A095929 
               A078482
%Y A151284 Adjacent sequences: A151281 A151282 A151283 this_sequence A151285 A151286 
               A151287
%K A151284 nonn,walk
%O A151284 0,2
%A A151284 Manuel Kauers (manuel(AT)kauers.de), Nov 18 2008