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%I #13 Jan 02 2024 08:55:16
%S 1,3,18,90,486,2538,13446,70794,373734,1970730,10396998,54839754,
%T 289283238,1525926762,8049179142,42458658570,223966125414,
%U 1181402279082,6231800342214,32872228375626,173398289233446,914661608207850
%N a(n)=3*a(n-1)+12*a(n-2) for n>=3, a(0)=1, a(1)=3, a(2)=18 .
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (3,12).
%F G.f.: (1-3*x^2)/(1-3*x-12*x^2) . a(n) = Sum_{k, 0<=k<=n}A122950(n,k)*3^k .
%t LinearRecurrence[{3,12},{1,3,18},30] (* _Harvey P. Dale_, Dec 20 2020 *)
%K easy,nonn
%O 0,2
%A _Philippe Deléham_, Dec 31 2007
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