a(n) = 9*n^3/2 - 21*n^2/2 + 8*n - 4.

Terms

a(0) =6a(1) =47a(2) =148a(3) =336a(4) =638a(5) =1081a(6) =1692a(7) =2498a(8) =3526a(9) =4803a(10) =6356a(11) =8212a(12) =10398a(13) =12941a(14) =15868a(15) =19206a(16) =22982a(17) =27223a(18) =31956a(19) =37208a(20) =43006a(21) =49377a(22) =56348a(23) =63946a(24) =72198a(25) =81131a(26) =90772a(27) =101148a(28) =112286a(29) =124213