Position of n-th 7 in A031298.

Terms

a(0) =7a(1) =24a(2) =44a(3) =64a(4) =84a(5) =104a(6) =124a(7) =131a(8) =133a(9) =135a(10) =137a(11) =139a(12) =141a(13) =143a(14) =144a(15) =145a(16) =147a(17) =149a(18) =164a(19) =184a(20) =211a(21) =241a(22) =271a(23) =301a(24) =331a(25) =361a(26) =391a(27) =401a(28) =404a(29) =407