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 A115307 #6 Mar 30 2012 18:50:53 %S A115307 1,2,3,4,5,6,13,12,11,10,9,8,7,20,19,18,17,16,15,14,27,26,25,24,23,22, %T A115307 21,34,33,32,31,30,29,28,41,40,39,38,37,36,35,48,47,46,45,44,43,42,97, %U A115307 96,95,94,93,92,91,90,89,88,87,86,85,84,83,82,81,80,79,78,77,76,75,74 %N A115307 a(n) = if n<7 then n else 7*a(floor(n/7)) + 6 - n mod 7. %C A115307 Self-inverse permutation of the natural numbers; %C A115307 A115310(n+5,6) = a(n); %C A115307 if n is written in base 7 representation, then a(n) is the value after replacing all digits d (but not the leading one) by 6-d. %H A115307 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %Y A115307 Cf. A054429, A115303, A115304, A115305, A115306, A115308, A115309, A106649. %K A115307 nonn,base %O A115307 1,2 %A A115307 _Reinhard Zumkeller_, Jan 20 2006