Position of n-th 7 in A031312.

Terms

a(0) =4a(1) =13a(2) =23a(3) =33a(4) =43a(5) =53a(6) =63a(7) =66a(8) =68a(9) =70a(10) =72a(11) =73a(12) =74a(13) =83a(14) =93a(15) =107a(16) =122a(17) =137a(18) =152a(19) =167a(20) =182a(21) =197a(22) =202a(23) =205a(24) =208a(25) =211a(26) =212a(27) =214a(28) =227a(29) =242