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

Terms

a(0) =0a(1) =1a(2) =15a(3) =54a(4) =130a(5) =255a(6) =441a(7) =700a(8) =1044a(9) =1485a(10) =2035a(11) =2706a(12) =3510a(13) =4459a(14) =5565a(15) =6840a(16) =8296a(17) =9945a(18) =11799a(19) =13870a(20) =16170a(21) =18711a(22) =21505a(23) =24564a(24) =27900a(25) =31525a(26) =35451a(27) =39690a(28) =44254a(29) =49155