1,2

a(n+1)-2a(n)= (-1)^n*A010716(n), n>1, period 2.

G.f.: x(1-3x-9x^2)/((1+x)(2x-1)). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 24 2008

a(n)= 11*2^(n-2)/3-5*(-1)^n/3, n>1. - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 24 2008

A020806 and its repeated differences in the followup rows start as follows:

..1,..4,..2,..8,..5,..7,..1,..4,..2,..8, <- A020806

..3,.-2,..6,.-3,..2,.-6,..3,.-2,..6,.-3, <- A131969

.-5,..8,.-9,..5,.-8,..9,.-5,..8,.-9,..5,

.13,-17,.14,-13,.17,-14,.13,-17,.14,-13,

-30,.31,-27,.30,-31,.27,-30,.31,-27,.30,

.61,-58,.57,-61,.58,-57,.61,-58,.57,-61,

The diagonal is 1,-2,-9,-13,-31,... which yields a(n) after signs are flipped.

Sequence in context: A115907 A063634 A163735 this_sequence A071343 A043401 A045920

Adjacent sequences: A144469 A144470 A144471 this_sequence A144473 A144474 A144475

sign

Paul Curtz (bpcrtz(AT)free.fr), Oct 10 2008, Oct 14 2008

Edited and extended, R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Oct 24 2008