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

Terms

a(0) =0a(1) =12a(2) =51a(3) =117a(4) =210a(5) =330a(6) =477a(7) =651a(8) =852a(9) =1080a(10) =1335a(11) =1617a(12) =1926a(13) =2262a(14) =2625a(15) =3015a(16) =3432a(17) =3876a(18) =4347a(19) =4845a(20) =5370a(21) =5922a(22) =6501a(23) =7107a(24) =7740a(25) =8400a(26) =9087a(27) =9801a(28) =10542a(29) =11310