[seqfan] Re: 4-12-28-60

[Richard Mathar]

http://list.seqfan.eu/pipermail/seqfan/2010-June/005124.html

D(n) is (with offset 1)
1,4,12,28,60,120,231,432,792,1430,2552,4512,7917,13804,23940,41328,71060,...
It has a simple (=non-interesting) generating function and linear recurrence
a(n)= +4*a(n-1) -4*a(n-2) -2*a(n-3) +4*a(n-4) -a(n-6)
    = A118425(n+2)-2*A118425(n-1)
G.f.: x*(1-2*x^3)/((x-1)^2*(x^2+x-1)^2)

The recurrence is known from A007574 which may give hints on whether
a similar construct is known in the literature.

RJM