A243004 a(n) = - (a(n-1) + 1) * a(n-2) with a(1) = a(2) = 1.

1, 1, -2, 1, 4, -5, 16, 85, -1376, 116875, 160821376, -18795998436875, 3022798331911925818624, 56816512721604915117046454761796875, -171744859879920049932215165532641220369502555067505818624

Offset

1,3

Links

G. C. Greubel, Table of n, a(n) for n = 1..20

Formula

0 = a(n) + a(n+2) + a(n)*a(n+1) for all n>0.

a(3*n) < 0, a(3*n + 1) > 0, a(3*n + 2) > 0, for all n>0.

Mathematica

RecurrenceTable[{a[1]==a[2]==1, a[n]==-(a[n-1]+1)a[n-2]}, a, {n, 15}] (* Harvey P. Dale, Dec 08 2014 *)

Prog

(PARI) {a(n) = if( n<3, n>0, - (a(n-1) + 1) * a(n-2))};
(Magma) I:=[1, 1]; [n le 2 select I[n] else -(1 + Self(n-1))*Self(n-2): n in [1..10]]; // G. C. Greubel, Aug 06 2018

Crossrefs

Sequence in context: A091232 A336398 A209337 * A375156 A137424 A083007

Adjacent sequences: A243001 A243002 A243003 * A243005 A243006 A243007

Keyword

sign

Author

Michael Somos, Aug 17 2014

Status

approved