a(n) = (1/2)*(n^3 + n*(n mod 2)).

Terms

a(0) =1a(1) =4a(2) =15a(3) =32a(4) =65a(5) =108a(6) =175a(7) =256a(8) =369a(9) =500a(10) =671a(11) =864a(12) =1105a(13) =1372a(14) =1695a(15) =2048a(16) =2465a(17) =2916a(18) =3439a(19) =4000a(20) =4641a(21) =5324a(22) =6095a(23) =6912a(24) =7825a(25) =8788a(26) =9855a(27) =10976a(28) =12209a(29) =13500