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A151368
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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, -1), (-1, 0), (-1, 1), (0, -1), (0, 1), (1, 0)}
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0
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1, 0, 2, 3, 12, 40, 145, 560, 2240, 9156, 38724, 166320, 728508, 3239808, 14595438, 66543477, 306511920, 1424916064, 6679435048, 31544500416, 149986398848, 717562911000, 3452381033556, 16696661334496, 81136327037620, 396022179418240, 1940898351416600, 9548613568549380, 47143311987432240
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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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[i, 1 + j, -1 + n] + aux[1 + i, -1 + j, -1 + n] + aux[1 + i, j, -1 + n] + aux[1 + i, 1 + j, -1 + n]]; Table[aux[0, 0, n], {n, 0, 25}]
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CROSSREFS
| Sequence in context: A012510 A012310 A082526 * A087650 A177699 A012514
Adjacent sequences: A151365 A151366 A151367 * A151369 A151370 A151371
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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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