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A151286
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, 0), (0, -1), (0, 1), (1, 0)}.
0
1, 2, 6, 20, 70, 260, 986, 3852, 15284, 61646, 251636, 1038026, 4320900, 18123780, 76544604, 325197844, 1389044326, 5961411840, 25695687106, 111190743966, 482866090476, 2103799954064, 9193627059292, 40287920890732, 177002193428102, 779506763324538, 3440547333117048, 15217327587907986
OFFSET
0,2
COMMENTS
Apparently a duplicate of A150127. - R. J. Mathar, Dec 13 2008
LINKS
M. Bousquet-Mélou 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[i, -1 + j, -1 + n] + aux[i, 1 + j, -1 + n] + aux[1 + i, 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
Cf. A150127.
Sequence in context: A151285 A150126 A150127 * A047126 A376792 A145138
KEYWORD
nonn,walk
AUTHOR
Manuel Kauers, Nov 18 2008
STATUS
approved