OFFSET
0,3
LINKS
Robert Israel, Table of n, a(n) for n = 0..200
A. Bostan and M. Kauers, 2008. Automatic Classification of Restricted Lattice Walks, ArXiv 0811.2899.
MAPLE
F:= proc(x, y, z, n) option remember; local t, s, u;
t:= 0:
if n = 0 then return 1 fi;
for s in [[-1, -1, 0], [-1, 0, 0], [0, 0, 1], [0, 1, -1], [1, -1, 0]] do
u:= [x, y, z]+s;
if min(u) >= 0 then t:= t + procname(op(u), n-1) fi
od;
t
end proc:
seq(F(0, 0, 0, n), n=0..40); # Robert Israel, Mar 27 2018
MATHEMATICA
aux[i_Integer, j_Integer, k_Integer, n_Integer] := Which[Min[i, j, k, n] < 0 || Max[i, j, k] > n, 0, n == 0, KroneckerDelta[i, j, k, n], True, aux[i, j, k, n] = aux[-1 + i, 1 + j, k, -1 + n] + aux[i, -1 + j, 1 + k, -1 + n] + aux[i, j, -1 + k, -1 + n] + aux[1 + i, j, k, -1 + n] + aux[1 + i, 1 + j, k, -1 + n]]; Table[Sum[aux[i, j, k, n], {i, 0, n}, {j, 0, n}, {k, 0, n}], {n, 0, 10}]
CROSSREFS
KEYWORD
nonn,walk
AUTHOR
Manuel Kauers, Nov 18 2008
STATUS
approved