login
a(n) = A050446(n, n) = A050447(n, n).
1

%I #7 Jun 12 2024 17:37:29

%S 1,2,6,30,190,1547,15106,173502,2286648,34053437,565424068,

%T 10358963615,207582616995,4516836844067,106059101583274,

%U 2673073911292478,71978776046880670,2062324447652722085,62647209605811093549,2011144064488835839006,68034719732835699646658

%N a(n) = A050446(n, n) = A050447(n, n).

%F a(n) = A373660(n, 0).

%o (Python)

%o from functools import cache

%o @cache

%o def T(n, k):

%o return T(n, k - 1) + sum(T(2 * j, k - 1) * T(n - 1 - 2 * j, k)

%o for j in range(1 + (n - 1) // 2)) if k > 0 else 1

%o def a(n): return T(n, n)

%o print([a(n) for n in range(21)])

%Y A050446, A050447, A373660.

%K nonn

%O 0,2

%A _Peter Luschny_, Jun 12 2024