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A151346
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Number of walks within N^2 (the first quadrant of Z^2) starting and ending at (0,0) and consisting of n steps taken from {(-1, 0), (-1, 1), (0, -1), (1, 0)}
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1
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1, 0, 1, 1, 2, 7, 10, 38, 89, 229, 752, 1873, 6009, 17746, 51970, 168199, 503489, 1609327, 5131184, 16183314, 53017947, 170708648, 559207257, 1846295302, 6075728984, 20284263554, 67649481468, 226890912838, 765669449228, 2585600921015, 8785174853897, 29918390234278, 102190450691351, 350429638975797
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,5
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LINKS
| M. Bousquet-Melou and M. Mishna, 2008. Walks with small steps in the quarter plane, ArXiv 0810.4387.
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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, j, -1 + n]]; Table[aux[0, 0, n], {n, 0, 25}]
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CROSSREFS
| Sequence in context: A084184 A015963 A056656 * A110739 A179117 A133154
Adjacent sequences: A151343 A151344 A151345 * A151347 A151348 A151349
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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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