a(n) = (1/24)*(n+1)*(3*n^3+59*n^2+358*n+648).

Terms

a(0) =0a(1) =27a(2) =89a(3) =203a(4) =389a(5) =670a(6) =1072a(7) =1624a(8) =2358a(9) =3309a(10) =4515a(11) =6017a(12) =7859a(13) =10088a(14) =12754a(15) =15910a(16) =19612a(17) =23919a(18) =28893a(19) =34599a(20) =41105a(21) =48482a(22) =56804a(23) =66148a(24) =76594a(25) =88225a(26) =101127a(27) =115389a(28) =131103a(29) =148364