[seqfan] Re: 4-12-28-60
Richard Mathar
mathar at strw.leidenuniv.nl
Wed Jun 23 12:38:11 CEST 2010
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
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