a(n)=least k such that the base 7 representation of n begins at s(k), where s=A031018.

Terms

a(0) =1a(1) =7a(2) =2a(3) =9a(4) =3a(5) =11a(6) =4a(7) =58a(8) =6a(9) =1a(10) =8a(11) =65a(12) =10a(13) =68a(14) =7a(15) =71a(16) =14a(17) =74a(18) =16a(19) =77a(20) =18a(21) =63a(22) =15a(23) =83a(24) =22a(25) =2a(26) =24a(27) =89a(28) =9a(29) =92