a(n) = 12*n + 9.

Terms

a(0) =9a(1) =21a(2) =33a(3) =45a(4) =57a(5) =69a(6) =81a(7) =93a(8) =105a(9) =117a(10) =129a(11) =141a(12) =153a(13) =165a(14) =177a(15) =189a(16) =201a(17) =213a(18) =225a(19) =237a(20) =249a(21) =261a(22) =273a(23) =285a(24) =297a(25) =309a(26) =321a(27) =333a(28) =345a(29) =357