Least common multiple of 3 and n^2+n+1.

Terms

a(0) =3a(1) =3a(2) =21a(3) =39a(4) =21a(5) =93a(6) =129a(7) =57a(8) =219a(9) =273a(10) =111a(11) =399a(12) =471a(13) =183a(14) =633a(15) =723a(16) =273a(17) =921a(18) =1029a(19) =381a(20) =1263a(21) =1389a(22) =507a(23) =1659a(24) =1803a(25) =651a(26) =2109a(27) =2271a(28) =813a(29) =2613