A108189 a(n) = (n-1)*(a(n-2)+a(n-3)).

0, 1, 1, 3, 8, 20, 66, 196, 688, 2358, 8840, 33506, 134376, 550498, 2350348, 10273110, 46413536, 214598786, 1020359628, 4959234118, 24699168280, 125571468666, 652484852756, 3456224649758, 18673351714128, 102717737562850

Offset: 1

Author

Roger L. Bagula, Jun 14 2005

Keywords

• nonn

Comments

Recurrence is similar to A000166 or A000931.

Links

• Robert Israel, Table of n, a(n) for n = 1..800

Crossrefs

Cf. A000166, A000213, A000931.

Programs

Maple

f:= gfun:-rectoproc({a(n) = (n-1)*(a(n-2)+a(n-3)),a(1)=0,a(2)=1,a(3)=1},a(n),remember):
map(f, [$1..40]); # Robert Israel, Feb 20 2017

Mathematica

F[1] = 0; F[2] = 1; F[3] = 1; F[n__] := F[n] = (n - 1)*( F[n - 2] + F[n - 3]) a = Table[F[n], {n, 1, 25}]

Formula

a(n) ~ (3/4)*sqrt(2) * exp(sqrt(n)-n/2-1/4)*n^(n/2-1/2) * (1-53/(24*sqrt(n))). - Vaclav Kotesovec, Dec 28 2012