a(n) = n*(14*n^2 - 21*n + 13)/6.

Terms

a(0) =0a(1) =1a(2) =9a(3) =38a(4) =102a(5) =215a(6) =391a(7) =644a(8) =988a(9) =1437a(10) =2005a(11) =2706a(12) =3554a(13) =4563a(14) =5747a(15) =7120a(16) =8696a(17) =10489a(18) =12513a(19) =14782a(20) =17310a(21) =20111a(22) =23199a(23) =26588a(24) =30292a(25) =34325a(26) =38701a(27) =43434a(28) =48538a(29) =54027