A122017 a(n) = if n even then a(n - 1) - (n - 1)*a(n - 2) otherwise 2*(a(n - 1) + (n - 1)*a(n - 2])).

1, 2, 1, 10, 7, 94, 59, 1246, 833, 21602, 14105, 460250, 305095, 11656190, 7689955, 341753230, 226403905, 11388911170, 7540044785, 425080891690, 281820040775, 17566875749150, 11648654892875, 796239842748350, 528320780212225

Offset

1,2

Links

Table of n, a(n) for n=1..25.

Mathematica

a[0] = 1; a[1] = 2; a[n_] := a[n] = If[Mod[n, 2] == 0, a[n - 1] - (n - 1)*a[n - 2], 2*(a[n - 1] + (n - 1)*a[n - 2])] b = Table[a[n], {n, 0, 30}]
nxt[{n_, a_, b_}]:={n+1, b, If[OddQ[n], b-n*a, 2(b+n*a)]}; NestList[nxt, {1, 1, 2}, 30][[All, 2]] (* Harvey P. Dale, Jun 12 2020 *)

Crossrefs

Cf. A000898, A121966.

Sequence in context: A225470 A081099 A213252 * A219900 A136233 A113088

Adjacent sequences: A122014 A122015 A122016 * A122018 A122019 A122020

Keyword

nonn

Author

Roger L. Bagula, Sep 11 2006

Extensions

Edited by N. J. A. Sloane, Sep 13 2006

Status

approved