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%I #4 Sep 08 2013 13:31:47
%S 1,3,3,15,3,87,-69,591,-1005,4551,-10581,37887,-101373,328695,-936933,
%T 2909103,-8530701,25985319,-77169525,233081439,-696098589,2094587223,
%U -6271178757,18838702095,-56465774637,169497987207,-508292635029
%N a(0)=1, a(1)=3,a(n)=6*a(n-2)-a(n-1).
%C a(n)/a(n-1) tends to -3.
%F G.f.: (1+4x)/(1+x-6x^2). a(n)= Sum_{k, 0<=k<=n}A112555(n,k)*2^k.
%F a(n) = (6*2^n-(-3)^n)/5. [From _Klaus Brockhaus_, Sep 26 2009]
%K sign
%O 0,2
%A _Philippe Deléham_, Sep 17 2009
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