

A151288


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), (1, 1), (0, 1), (1, 1), (1, 0)}


0



1, 2, 6, 22, 84, 336, 1392, 5912, 25580, 112324, 499312, 2242188, 10154664, 46324964, 212664488, 981653620, 4553218968, 21209894268, 99178882232, 465362985740, 2190341893320, 10338437549876, 48922967035664, 232055129413436, 1103080339515552, 5253968486241476, 25070738463476960, 119836239979700524
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OFFSET

0,2


LINKS

Table of n, a(n) for n=0..27.
M. BousquetMÃ©lou and M. Mishna, 2008. Walks with small steps in the quarter plane, ArXiv 0810.4387.
A. Bostan and M. Kauers, 2008. Automatic Classification of Restricted Lattice Walks, ArXiv 0811.2899.


MATHEMATICA

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] + aux[1 + i, 1 + j, 1 + n]]; Table[Sum[aux[i, j, n], {i, 0, n}, {j, 0, n}], {n, 0, 25}]


CROSSREFS

Sequence in context: A245904 A128723 A150244 * A150245 A150246 A055700
Adjacent sequences: A151285 A151286 A151287 * A151289 A151290 A151291


KEYWORD

nonn,walk


AUTHOR

Manuel Kauers, Nov 18 2008


STATUS

approved



