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A151396
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Number of walks within N^2 (the first quadrant of Z^2) starting at (0,0), ending on the vertical axis and consisting of n steps taken from {(-1, -1), (0, -1), (0, 1), (1, 1)}.
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0
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1, 1, 3, 6, 21, 52, 193, 532, 2034, 5985, 23283, 71610, 281688, 894660, 3545919, 11541114, 45988056, 152599174, 610459630, 2057627572, 8255756937, 28190598072, 113365682625, 391366771432, 1576636806694, 5494187368180, 22164611973120, 77867785091880, 314485620041700, 1112719363776720, 4498007052780945
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OFFSET
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0,3
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LINKS
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MATHEMATICA
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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[i, 1 + j, -1 + n] + aux[1 + i, 1 + j, -1 + n]]; Table[Sum[aux[0, k, n], {k, 0, n}], {n, 0, 25}]
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CROSSREFS
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KEYWORD
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nonn,walk
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AUTHOR
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STATUS
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approved
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