a(n) = 18*(n - 2)*(2*n - 5).

Terms

a(0) =0a(1) =18a(2) =108a(3) =270a(4) =504a(5) =810a(6) =1188a(7) =1638a(8) =2160a(9) =2754a(10) =3420a(11) =4158a(12) =4968a(13) =5850a(14) =6804a(15) =7830a(16) =8928a(17) =10098a(18) =11340a(19) =12654a(20) =14040a(21) =15498a(22) =17028a(23) =18630a(24) =20304a(25) =22050a(26) =23868a(27) =25758a(28) =27720a(29) =29754