a(n) = [x^n] (4*x^2 + x - 1)/(4*x^3 + 3*x^2 + 2*x - 1).

Terms

a(0) =1a(1) =1a(2) =1a(3) =9a(4) =25a(5) =81a(6) =273a(7) =889a(8) =2921a(9) =9601a(10) =31521a(11) =103529a(12) =340025a(13) =1116721a(14) =3667633a(15) =12045529a(16) =39560841a(17) =129928801a(18) =426722241a(19) =1401474249a(20) =4602830425a(21) =15116972561a(22) =49648333393a(23) =163058906169a(24) =535530702761