a(n) = A120963(2*n)/2.

Terms

a(0) =3a(1) =12a(2) =39a(3) =112a(4) =292a(5) =710a(6) =1629a(7) =3567a(8) =7505a(9) =15266a(10) =30140a(11) =57983a(12) =108981a(13) =200625a(14) =362433a(15) =643653a(16) =1125269a(17) =1939149a(18) =3297411a(19) =5538254a(20) =9195371a(21) =15104245a(22) =24561098a(23) =39562657a(24) =63160404a(25) =99987453a(26) =157029090a(27) =244754385a(28) =378754786a(29) =582124254