a(n) = (n^4 - n^3 + 4*n^2 + 2)/2.

Terms

a(0) =1a(1) =3a(2) =13a(3) =46a(4) =129a(5) =301a(6) =613a(7) =1128a(8) =1921a(9) =3079a(10) =4701a(11) =6898a(12) =9793a(13) =13521a(14) =18229a(15) =24076a(16) =31233a(17) =39883a(18) =50221a(19) =62454a(20) =76801a(21) =93493a(22) =112773a(23) =134896a(24) =160129a(25) =188751a(26) =221053a(27) =257338a(28) =297921a(29) =343129