A140505 Second differences of Jacobsthal sequence A001045, pairs with even and odd indices swapped.

2, -1, 4, 0, 12, 4, 44, 20, 172, 84, 684, 340, 2732, 1364, 10924, 5460, 43692, 21844, 174764, 87380, 699052, 349524, 2796204, 1398100, 11184812, 5592404, 44739244, 22369620, 178956972, 89478484, 715827884, 357913940, 2863311532, 1431655764, 11453246124

Offset: 0

Author

Paul Curtz, Jun 30 2008

Keywords

• sign
• less

Comments

The second differences are -1, 2, 0, 4, 4, 12, 20, 44, ... (-1)^(n+1)*A084247(n), essentially A097073, which are listed here with -1 <=> 2, 0 <=> 4 etc. swapped in pairs.

Formula

a(n) = 4*A092808(n-2), n>1.

a(n+1) - 2a(n) = (-1)^n*A140504(n).

O.g.f.: (2+x-5x^2)/[(1+x)(1-2x)(1+2x)]. - R. J. Mathar, Jul 08 2008

Extensions

Edited by R. J. Mathar, Jul 08 2008