Position of n-th 4 in A031027.

Terms

a(0) =11a(1) =21a(2) =22a(3) =27a(4) =37a(5) =38a(6) =39a(7) =56a(8) =64a(9) =68a(10) =79a(11) =93a(12) =94a(13) =96a(14) =100a(15) =105a(16) =106a(17) =108a(18) =122a(19) =125a(20) =130a(21) =132a(22) =137a(23) =140a(24) =154a(25) =160a(26) =163a(27) =171a(28) =178a(29) =184