%I
%S 1,2,3,5,9,16,30,58,113,223,443,882,1760,3516,7027,14049,28093,56180,
%T 112354,224702,449397,898787,1797567,3595126,7190244,14380480,
%U 28760951,57521893,115043777,230087544,460175078,920350146,1840700281,3681400551
%N a(n) = 2*a(n1)  [(n+1)/3] for n>0 with a(0) = 1.
%F G.f. A(x) = (1  x^2*(1+x+x^2)/(1x^3)^2 )/(12*x).
%o (PARI) {a(n)=if(n==0,1,2*a(n1)((n+1)\3))}
%Y Cf. A136219.
%K nonn
%O 0,2
%A _Paul D. Hanna_, Dec 23 2007
