A031015 a(n)=least k such that base 7 representation of n begins at s(k), where s=A031007.

1, 2, 3, 4, 5, 6, 20, 8, 1, 12, 14, 16, 18, 34, 11, 24, 2, 28, 30, 32, 48, 13, 27, 40, 3, 44, 46, 62, 15, 29, 43, 56, 4, 60, 76, 17, 31, 45, 59, 72, 5, 6, 19, 33, 47, 61, 75, 88, 237, 94, 20, 153, 174, 195, 216, 93, 8, 9, 119, 122, 125, 128, 96