a(n) = 12*n + 3.

Terms

a(0) =3a(1) =15a(2) =27a(3) =39a(4) =51a(5) =63a(6) =75a(7) =87a(8) =99a(9) =111a(10) =123a(11) =135a(12) =147a(13) =159a(14) =171a(15) =183a(16) =195a(17) =207a(18) =219a(19) =231a(20) =243a(21) =255a(22) =267a(23) =279a(24) =291a(25) =303a(26) =315a(27) =327a(28) =339a(29) =351