Position of n-th 4 in A031076.

Terms

a(0) =4a(1) =18a(2) =36a(3) =54a(4) =63a(5) =65a(6) =67a(7) =69a(8) =71a(9) =72a(10) =73a(11) =75a(12) =77a(13) =79a(14) =90a(15) =108a(16) =126a(17) =144a(18) =167a(19) =194a(20) =221a(21) =248a(22) =262a(23) =265a(24) =268a(25) =271a(26) =274a(27) =275a(28) =277a(29) =280