G.f. sum{k>=0, (x^2/(1-x)^3)^(2^k-1)}.

Terms

a(0) =1a(1) =0a(2) =1a(3) =3a(4) =6a(5) =10a(6) =16a(7) =30a(8) =73a(9) =201a(10) =540a(11) =1342a(12) =3069a(13) =6513a(14) =12962a(15) =24436a(16) =44109a(17) =77489a(18) =136749a(19) =256791a(20) =550190a(21) =1378554a(22) =3843807a(23) =11096833a(24) =31607566a(25) =86892690a(26) =228901270a(27) =577458936a(28) =1397828943a(29) =3255832291