a(n)=least k such that base 7 representation of n begins at s(k), where s=A031007.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =6a(6) =20a(7) =8a(8) =1a(9) =12a(10) =14a(11) =16a(12) =18a(13) =34a(14) =11a(15) =24a(16) =2a(17) =28a(18) =30a(19) =32a(20) =48a(21) =13a(22) =27a(23) =40a(24) =3a(25) =44a(26) =46a(27) =62a(28) =15a(29) =29