Position of n-th 4 in A031312.

Terms

a(0) =36a(1) =38a(2) =40a(3) =42a(4) =44a(5) =157a(6) =160a(7) =163a(8) =166a(9) =169a(10) =307a(11) =310a(12) =313a(13) =316a(14) =319a(15) =457a(16) =460a(17) =463a(18) =466a(19) =469a(20) =546a(21) =549a(22) =552a(23) =555a(24) =558a(25) =561a(26) =564a(27) =567a(28) =570a(29) =573