%I A072130
%S A072130 0,1,5,14,37,99,260,681,1785,4674,12237,32039,83880,219601,574925,
%T A072130 1505174,3940597,10316619,27009260,70711161,185124225,484661514,
%U A072130 1268860317,3321919439,8696898000,22768774561,59609425685,156059502494
%N A072130 a(n+1) -3*a(n) + a(n-1) = (2/3)(1+w^(n+1)+w^(2n+2)); a(1) = 0, a(2) = 
               1; where w is the imaginary cubic root of unity.
%C A072130 w = exp(2Pi*I/3) = (-1-Sqrt(-3))/2.
%t A072130 a[1] = 0; a[2] = 1; w = Exp[2Pi*I/3]; a[n_] := (2/3)(1 + w^n + w^(2n)) 
               + 3a[n - 1] - a[n - 2]; Table[ Simplify[ a[n]], {n, 1, 28}]
%Y A072130 Cf. A071618.
%Y A072130 Sequence in context: A048745 A127980 A054486 this_sequence A045553 A111715 
               A024525
%Y A072130 Adjacent sequences: A072127 A072128 A072129 this_sequence A072131 A072132 
               A072133
%K A072130 nonn
%O A072130 1,3
%A A072130 Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 24 2002