Position of n-th 4 in A031298.

Terms

a(0) =4a(1) =18a(2) =38a(3) =58a(4) =71a(5) =73a(6) =75a(7) =77a(8) =78a(9) =79a(10) =81a(11) =83a(12) =85a(13) =87a(14) =89a(15) =98a(16) =118a(17) =138a(18) =158a(19) =178a(20) =202a(21) =232a(22) =262a(23) =292a(24) =311a(25) =314a(26) =317a(27) =320a(28) =322a(29) =323