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A151280
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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, 0)}
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0
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1, 2, 5, 15, 47, 150, 495, 1672, 5698, 19636, 68470, 240342, 848258, 3012899, 10753669, 38519879, 138501666, 499728140, 1807946861, 6557502077, 23843549009, 86880613032, 317170036587, 1160001218633, 4249640363945, 15591664759190, 57285869534363, 210757677563396, 776332308628500, 2862899274870651
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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LINKS
| M. Bousquet-Melou 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.
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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[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}]
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CROSSREFS
| Sequence in context: A148362 A143094 A058495 * A149914 A071735 A148363
Adjacent sequences: A151277 A151278 A151279 * A151281 A151282 A151283
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KEYWORD
| nonn,walk
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AUTHOR
| Manuel Kauers (manuel(AT)kauers.de), Nov 18 2008
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