Position of n-th 7 in A031057.

Terms

a(0) =4a(1) =12a(2) =20a(3) =28a(4) =36a(5) =44a(6) =52a(7) =53a(8) =55a(9) =57a(10) =59a(11) =60a(12) =72a(13) =84a(14) =96a(15) =108a(16) =120a(17) =132a(18) =144a(19) =146a(20) =149a(21) =152a(22) =155a(23) =156a(24) =168a(25) =180a(26) =192a(27) =204a(28) =216a(29) =228