OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..400
FORMULA
a(n) ~ c * 6^(3*n) / n, where c = 0.000020280187096503586851533... . - Vaclav Kotesovec, Oct 14 2016
MAPLE
g():= combinat[permute]([0, -1, 2]):
b:= proc(l) option remember; `if`(l=[1$3], 1, add((p->
`if`(p[1]<0, 0, b(p)))(sort(l-x)), x=g()))
end:
a:= n-> b([n$3]):
seq(a(n), n=0..20);
MATHEMATICA
g = Permutations[{0, -1, 2}];
b[l_] := b[l] = If[l == {1, 1, 1}, 1, Sum[Function[p, If[p[[1]] < 0, 0, b[p]]][Sort[l - x]], {x, g}]];
a[n_] := b[{n, n, n}];
Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Mar 29 2017, translated from Maple *)
CROSSREFS
KEYWORD
nonn,walk
AUTHOR
Alois P. Heinz, Oct 07 2016
STATUS
approved