a(n) = (9/2)*(n-1)*(n-2)*(n-3).

Terms

a(0) =0a(1) =0a(2) =0a(3) =27a(4) =108a(5) =270a(6) =540a(7) =945a(8) =1512a(9) =2268a(10) =3240a(11) =4455a(12) =5940a(13) =7722a(14) =9828a(15) =12285a(16) =15120a(17) =18360a(18) =22032a(19) =26163a(20) =30780a(21) =35910a(22) =41580a(23) =47817a(24) =54648a(25) =62100a(26) =70200a(27) =78975a(28) =88452a(29) =98658