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A151335
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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, -1)}
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0
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1, 0, 0, 1, 0, 1, 5, 1, 18, 43, 47, 313, 570, 1480, 5847, 11715, 41194, 124918, 317707, 1120909, 3159179, 9581991, 31624946, 92407981, 300936377, 954921610, 2965630143, 9769316877, 30986916602, 100406899586, 329864837841, 1066298792633, 3525879988702, 11612179660287, 38300799541992, 127788972039783
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,7
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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, 1 + 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: A104174 A050400 A008971 * A055584 A193861 A193857
Adjacent sequences: A151332 A151333 A151334 * A151336 A151337 A151338
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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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