Position of n-th 4 in A031007.

Terms

a(0) =4a(1) =15a(2) =29a(3) =43a(4) =50a(5) =52a(6) =54a(7) =56a(8) =57a(9) =58a(10) =60a(11) =62a(12) =71a(13) =85a(14) =103a(15) =124a(16) =145a(17) =166a(18) =176a(19) =179a(20) =182a(21) =185a(22) =187a(23) =188a(24) =191a(25) =194a(26) =208a(27) =229a(28) =250a(29) =271