Position of n-th 4 in A031324.

Terms

a(0) =11a(1) =17a(2) =18a(3) =38a(4) =39a(5) =50a(6) =62a(7) =81a(8) =92a(9) =100a(10) =104a(11) =119a(12) =134a(13) =138a(14) =146a(15) =164a(16) =174a(17) =185a(18) =192a(19) =196a(20) =199a(21) =201a(22) =202a(23) =208a(24) =217a(25) =244a(26) =259a(27) =262a(28) =285a(29) =328