A047907 a(n+1) = a(n) - n (if n is even), a(n+1) = a(n) * n (if n is odd).

1, 1, -1, -3, -7, -35, -41, -287, -295, -2655, -2665, -29315, -29327, -381251, -381265, -5718975, -5718991, -97222847, -97222865, -1847234435, -1847234455, -38791923555, -38791923577, -892214242271, -892214242295, -22305356057375, -22305356057401

Offset

1,4

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..500

Formula

a(n) = a(n-1)*(n-1)^((n-1) mod 2)-(n-1)*(n mod 2) for n > 1, with a(1) = 1. - Wesley Ivan Hurt, Jun 27 2026

Maple

a:= proc(n) option remember; `if`(n=1, 1,
      `if`(irem(n, 2)=1, a(n-1) -(n-1), a(n-1) *(n-1)))
    end:
seq(a(n), n=1..30);  # Alois P. Heinz, Jun 24 2013

Mathematica

nxt[{n_, a_}]:={n+1, If[OddQ[n], a-(n+1), a(n+1)]}; Transpose[NestList[nxt, {0, 1}, 30]][[2]] (* Harvey P. Dale, Jun 24 2013 *)
(* Alternative: *)
a[n_]:=a[n-1]*(n-1)^Mod[n-1, 2]-(n-1)*Mod[n, 2]; a[1]:=1; Table[a[n], {n, 40}] (* Wesley Ivan Hurt, Jun 27 2026 *)

Prog

(Haskell)
a047907 n = a047907_list !! (n-1)
a047907_list = 1 : zipWith uncurry
                           (cycle [(*), (-)]) (zip a047907_list [1..])
-- Reinhard Zumkeller, Nov 13 2013, Dec 17 2011

Crossrefs

Cf. A000124, A000142, A047906.

Sequence in context: A334314 A179115 A299300 * A328420 A336012 A212417

Adjacent sequences: A047904 A047905 A047906 * A047908 A047909 A047910

Keyword

sign,nice,easy,changed

Author

Miklos SZABO (mike(AT)ludens.elte.hu)

Status

approved