Position of n-th 3 in A031007.

Terms

a(0) =3a(1) =13a(2) =27a(3) =36a(4) =38a(5) =40a(6) =41a(7) =42a(8) =44a(9) =46a(10) =48a(11) =55a(12) =69a(13) =83a(14) =100a(15) =121a(16) =142a(17) =155a(18) =158a(19) =161a(20) =163a(21) =164a(22) =167a(23) =170a(24) =173a(25) =184a(26) =205a(27) =226a(28) =247a(29) =268