A009725 Expansion of e.g.f.: tan(x)*(1+x).

0, 1, 2, 2, 8, 16, 96, 272, 2176, 7936, 79360, 353792, 4245504, 22368256, 313155584, 1903757312, 30460116992, 209865342976, 3777576173568, 29088885112832, 581777702256640, 4951498053124096, 108932957168730112, 1015423886506852352, 24370173276164456448

Offset: 0

Author

R. H. Hardin

Keywords

• nonn
• easy

Crossrefs

a(2n) = A009752(n), a(2n+1) = A000182(n+1).

Programs

Mathematica

With[{nn=30},CoefficientList[Series[Tan[x]*(1+x),{x,0,nn}],x] Range[0,nn]!] (* Harvey P. Dale, Oct 29 2020 *)

Formula

E.g.f.: x*(1+x)*Q(0), where Q(k) = 1 - x^2/(x^2 - (2*k+1)*(2*k+3)/Q(k+1) ); (continued fraction). - Sergei N. Gladkovskii, Dec 16 2013

Extensions

Definition clarified and prior Mathematica program replaced by Harvey P. Dale, Oct 29 2020