Position of n-th 3 in A031076.

Terms

a(0) =3a(1) =16a(2) =34a(3) =45a(4) =47a(5) =49a(6) =51a(7) =52a(8) =53a(9) =55a(10) =57a(11) =59a(12) =61a(13) =70a(14) =88a(15) =106a(16) =124a(17) =142a(18) =164a(19) =191a(20) =218a(21) =235a(22) =238a(23) =241a(24) =244a(25) =245a(26) =247a(27) =250a(28) =253a(29) =256