This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A167456 #4 Apr 04 2015 21:34:04 %S A167456 2,6,7,8,9,66,660,700,701,702,703,704,705,707,708,709,710,711,712,713, %T A167456 714,715,717,718,719,760,770,771,772,773,774,775,777,778,779,780,781, %U A167456 782,783,784,785,787,788,789,790,791,792,793,794,795,797,798,799,800 %N A167456 Smallest sequence which lists the position of digits "6" in the sequence. %C A167456 The lexicographically earliest sequence such that a(1),a(2),a(3),... is the (increasing) list of the positions of digits "6" in the string obtained by concatenating all these terms, written in base 10. %e A167456 We cannot have a(1)=1 (since then there's no "6" in the first place), but a(1)=2 is possible. %e A167456 Then a(2) must start with a digit "6", so a(2)=6 is the smallest possible choice. %e A167456 This allows us to go on with a(3)=7, a(4)=8, a(5)=9, but then must be follow 4 digits "6" (the 6th through 9th digit of the sequence), so a(6)=66 and a(7)=660 are the smallest possible choices. %e A167456 Then the reasoning continues in analogy with A167452-A167455. %o A167456 (PARI) concat([ [2,6,7,8,9,66,660], vector((66-9)\3-1,i,700-(i<=6)+i+(i>=16)), [760], select(x->x%10-6 & x\10%10-6,vector((660-66)\3+10,i,770+i-1)) ]) %Y A167456 Cf. A098645, A167519, A167520, A167452 - A167455. %K A167456 base,nonn %O A167456 1,1 %A A167456 _M. F. Hasler_, Nov 19 2009