a(n) = 9*(n-2)^2*(n^2-2*n-1)/2.

Terms

a(0) =0a(1) =9a(2) =126a(3) =567a(4) =1656a(5) =3825a(6) =7614a(7) =13671a(8) =22752a(9) =35721a(10) =53550a(11) =77319a(12) =108216a(13) =147537a(14) =196686a(15) =257175a(16) =330624a(17) =418761a(18) =523422a(19) =646551a(20) =790200a(21) =956529a(22) =1147806a(23) =1366407a(24) =1614816a(25) =1895625a(26) =2211534a(27) =2565351a(28) =2959992a(29) =3398481