A025271 a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ...+ a(n-1)*a(1) for n >= 5.

1, 1, 2, 1, 6, 18, 52, 165, 518, 1646, 5308, 17258, 56604, 187108, 622632, 2084461, 7016134, 23730006, 80610156, 274911614, 940915892, 3230919164, 11127525464, 38429281122, 133052559772, 461740643276, 1605877668824, 5596283069300