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Sum k=0..n, C(n-k, floor(k/2))4^k.
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%I #8 Jun 13 2015 00:51:30

%S 1,5,5,21,101,181,517,2133,5029,13301,47429,127893,340709,1099573,

%T 3145861,8597205,26190373,76524149,214079429,633125397,1857511781,

%U 5282782645,15412788997,45132977493,129657499813,376262123765

%N Sum k=0..n, C(n-k, floor(k/2))4^k.

%C The sequence sum{k=0..n, C(n-k,floor(k/2))r^k} has g.f. (1+rx)/(1-x-r^2x^3).

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,16)

%F G.f. : (1+4x)/(1-x-16x^3); a(n)=a(n-1)+16a(n-3).

%t LinearRecurrence[{1,0,16},{1,5,5},30] (* _Harvey P. Dale_, Sep 15 2011 *)

%Y Cf. A097333, A097334, A097335.

%K easy,nonn

%O 0,2

%A _Paul Barry_, Aug 05 2004