a(n) = n^2*(1+n)*(1+n^2)/4.

Terms

a(0) =1a(1) =15a(2) =90a(3) =340a(4) =975a(5) =2331a(6) =4900a(7) =9360a(8) =16605a(9) =27775a(10) =44286a(11) =67860a(12) =100555a(13) =144795a(14) =203400a(15) =279616a(16) =377145a(17) =500175a(18) =653410a(19) =842100a(20) =1072071a(21) =1349755a(22) =1682220a(23) =2077200a(24) =2543125a(25) =3089151a(26) =3725190a(27) =4461940a(28) =5310915a(29) =6284475