Position of n-th 4 in A031045.

Terms

a(0) =4a(1) =16a(2) =32a(3) =48a(4) =57a(5) =59a(6) =61a(7) =63a(8) =64a(9) =65a(10) =67a(11) =69a(12) =71a(13) =80a(14) =96a(15) =112a(16) =132a(17) =156a(18) =180a(19) =204a(20) =217a(21) =220a(22) =223a(23) =226a(24) =228a(25) =229a(26) =232a(27) =235a(28) =238a(29) =252