|
%I #5 Jun 13 2015 00:51:50
%S 1,1,4,19,55,220,793,2845,10480,37963,138259,503608,1831969,6669865,
%T 24276892,88362451,321640831,1170726484,4261339801,15510894949,
%U 56458080328,205502135851,748007984827,2722677076336,9910284168961
%N Sum binomial(2n-2k,2k)3^k, k=0..floor(n/2).
%C In general, sum{k=0..floor(n/2), C(2n-2k,2k)a^k*b^(n-k)} has expansion (1-bx-abx^2)/(1-2bx-(2ab-b^2)x^2-2ab^2*x^3+(ab)^2*x^4).
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,5,6,-9).
%F G.f.: (1-x-3x^2)/(1-2x-5x^2-6x^3+9x^4); a(n)=2a(n-1)+5a(n-2)+6a(n-3)-9a(n-4).
%K easy,nonn
%O 0,3
%A _Paul Barry_, Jun 04 2005
|
