a(n) = 90*binomial(n,6) + 18*binomial(n,4) + 3*binomial(n,2) + 1.

Terms

a(0) =1a(1) =1a(2) =4a(3) =10a(4) =37a(5) =121a(6) =406a(7) =1324a(8) =3865a(9) =9937a(10) =22816a(11) =47686a(12) =92269a(13) =167545a(14) =288562a(15) =475336a(16) =753841a(17) =1157089a(18) =1726300a(19) =2512162a(20) =3576181a(21) =4992121a(22) =6847534a(23) =9245380a(24) =12305737a(25) =16167601a(26) =20990776a(27) =26957854a(28) =34276285a(29) =43180537