Position of n-th 3 in A031100.

Terms

a(0) =2a(1) =18a(2) =23a(3) =25a(4) =27a(5) =29a(6) =31a(7) =36a(8) =54a(9) =72a(10) =97a(11) =120a(12) =123a(13) =124a(14) =126a(15) =129a(16) =151a(17) =178a(18) =205a(19) =232a(20) =240a(21) =243a(22) =246a(23) =249a(24) =252a(25) =259a(26) =286a(27) =313a(28) =320a(29) =323