a(n) = 216*n - 12.

Terms

a(0) =204a(1) =420a(2) =636a(3) =852a(4) =1068a(5) =1284a(6) =1500a(7) =1716a(8) =1932a(9) =2148a(10) =2364a(11) =2580a(12) =2796a(13) =3012a(14) =3228a(15) =3444a(16) =3660a(17) =3876a(18) =4092a(19) =4308a(20) =4524a(21) =4740a(22) =4956a(23) =5172a(24) =5388a(25) =5604a(26) =5820a(27) =6036a(28) =6252a(29) =6468