OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1663
MAPLE
b:= proc(x, y) option remember; `if`(x=0, [1, 0],
add(add((p-> p+[0, p[1]*h*(2*y-v)])(b(x-h, y-v)),
h=1..min(x-y+v, max(1, y-v))), v=-1..min(y, 1)))
end:
a:= n-> b(n, 0)[2]:
seq(a(n), n=0..30);
MATHEMATICA
b[x_, y_] := b[x, y] = If[x == 0, {1, 0},
Sum[Sum[Function[p, p + {0, p[[1]]*h*(2*y - v)}][b[x - h, y - v]],
{h, 1, Min[x - y + v, Max[1, y - v]]}], {v, -1, Min[y, 1]}]];
a[n_] := b[n, 0][[2]];
Table[a[n], {n, 0, 30}] (* Jean-François Alcover, Mar 24 2022, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Oct 12 2020
STATUS
approved