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%I #3 Mar 30 2012 17:39:46
%S 1,5,91,410,7381,33215,597871,2690420,48427561,217924025,3922632451,
%T 17651846030,317733228541,1429799528435,25736391511831,
%U 115813761803240,2084647712458321,9380914706062445,168856464709124011
%N A threes sequence that gets more even factors out: a(n)=(3^n - 1)*(3^n + 1)/2^(4 - Mod[n, 2]).
%F a(n)=(3^n - 1)*(3^n + 1)/2^(4 - Mod[n, 2]).
%F a(n)=82*a(n-2)-81*a(n-4). G.f.: (1+5x+9x^2)/((1-x)(1-9x)(1+x)(1+9x)). [From _R. J. Mathar_, Dec 04 2008]
%t Clear[a, n];
%t a[n_] :=(3^n - 1)*(3^n + 1)/2^(4 - Mod[n, 2]);
%t Table[a[n], {n, 0, 30}]
%Y A003462, A002452
%K nonn
%O 0,2
%A _Roger L. Bagula_, Dec 02 2008
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