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Expansion of 1/(1-2x-3x^4).
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%I #6 Jun 13 2015 00:51:34

%S 1,2,4,8,19,44,100,224,505,1142,2584,5840,13195,29816,67384,152288,

%T 344161,777770,1757692,3972248,8976979,20287268,45847612,103611968,

%U 234154873,529171550,1195885936,2702607776,6107680171,13802874992

%N Expansion of 1/(1-2x-3x^4).

%C In general 1/(1-a*x-b*x^4) expands to sum{k=0..floor(n/4),C(n-3k,k)b^(n-3k)(a/b)^(n-4k)}.

%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,0,3).

%F a(n)=2a(n-1)+3a(n-4); a(n)=sum{k=0..floor(n/4), binomial(n-3k, k)3^(n-3k)(2/3)^(n-4k)}.

%Y Cf. A099525.

%K easy,nonn

%O 0,2

%A _Paul Barry_, Oct 20 2004