a(n) = n*(n + 1)*(5*n - 4)/2.

Terms

a(0) =0a(1) =1a(2) =18a(3) =66a(4) =160a(5) =315a(6) =546a(7) =868a(8) =1296a(9) =1845a(10) =2530a(11) =3366a(12) =4368a(13) =5551a(14) =6930a(15) =8520a(16) =10336a(17) =12393a(18) =14706a(19) =17290a(20) =20160a(21) =23331a(22) =26818a(23) =30636a(24) =34800a(25) =39325a(26) =44226a(27) =49518a(28) =55216a(29) =61335