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A151310
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), (-1, 0), (0, 1), (1, -1), (1, 1)}
1
1, 2, 9, 37, 181, 869, 4430, 22640, 118808, 627275, 3358307, 18087833, 98248087, 536372711, 2945032779, 16237200915, 89896571332, 499383074373, 2783038880080, 15552412965005, 87134774936870, 489297438647055, 2753406974342080, 15523739339340106, 87677875795392958, 496006562740402954
OFFSET
0,2
LINKS
M. Bousquet-Mélou 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.
MAPLE
steps:= [[-1, -1], [-1, 1], [-1, 0], [0, 1], [1, -1], [1, 1]]:
f:= proc(n, p) option remember; local t;
if n <= min(p) then return 6^n fi;
add(procname(n-1, t), t=remove(has, map(`+`, steps, p), -1));
end proc:
map(f, [$0..100], [0, 0]); # Robert Israel, Jun 11 2019
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[-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] + aux[1 + i, 1 + j, -1 + n]]; Table[Sum[aux[i, j, n], {i, 0, n}, {j, 0, n}], {n, 0, 25}]
CROSSREFS
Sequence in context: A150990 A150991 A150992 * A000663 A364088 A218942
KEYWORD
nonn,walk
AUTHOR
Manuel Kauers, Nov 18 2008
STATUS
approved