A122876 a(0)=1, a(1)=1, a(2)=2, a(n) = a(n-1) - a(n-2) for n>2.

1, 1, 2, 1, -1, -2, -1, 1, 2, 1, -1, -2, -1, 1, 2, 1, -1, -2, -1, 1, 2, 1, -1, -2, -1, 1, 2, 1, -1, -2, -1, 1, 2, 1, -1, -2, -1, 1, 2, 1, -1, -2, -1, 1, 2, 1, -1, -2, -1, 1, 2, 1, -1, -2, -1, 1, 2, 1, -1, -2, -1, 1, 2, 1, -1, -2, -1, 1, 2, 1, -1, -2, -1, 1, 2, 1, -1, -2, -1

Offset: 0

Author

Philippe Deléham, Oct 24 2006

Keywords

• sign
• easy

Comments

Essentially the same as A057079, A087204 and A100051.

Links

• Index entries for linear recurrences with constant coefficients, signature (1,-1).

Crossrefs

Cf. A055830, A057079, A087204, A100051.

Programs

Mathematica

LinearRecurrence[{1,-1}, {1,1,2}, 50] (* G. C. Greubel, May 03 2017; corrected by Georg Fischer, Apr 02 2019 *)
(* or *) CoefficientList[Series[(1 + 2*x^2)/(1 - x + x^2), {x,0,50}], x] (* G. C. Greubel, May 03 2017 *)

PARI

my(x='x+O('x^50)); Vec((1+2*x^2)/(1-x+x^2)) \\ G. C. Greubel, May 03 2017

Formula

a(n) = Sum_{k=0..floor(n/2)} (-2)^k*A055830(n-k,k).

G.f.: (1+2*x^2)/(1-x+x^2).