a(n) = 3*(n - 2)*(5*n -11).

Terms

a(0) =0a(1) =12a(2) =54a(3) =126a(4) =228a(5) =360a(6) =522a(7) =714a(8) =936a(9) =1188a(10) =1470a(11) =1782a(12) =2124a(13) =2496a(14) =2898a(15) =3330a(16) =3792a(17) =4284a(18) =4806a(19) =5358a(20) =5940a(21) =6552a(22) =7194a(23) =7866a(24) =8568a(25) =9300a(26) =10062a(27) =10854a(28) =11676a(29) =12528