3n^3 - 2n^2 + n - 1.

Terms

a(0) =1a(1) =17a(2) =65a(3) =163a(4) =329a(5) =581a(6) =937a(7) =1415a(8) =2033a(9) =2809a(10) =3761a(11) =4907a(12) =6265a(13) =7853a(14) =9689a(15) =11791a(16) =14177a(17) =16865a(18) =19873a(19) =23219a(20) =26921a(21) =30997a(22) =35465a(23) =40343a(24) =45649a(25) =51401a(26) =57617a(27) =64315a(28) =71513a(29) =79229