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 A249506 #8 Oct 30 2014 19:29:58 %S A249506 1,7,2,8,3,9,4,10,5,6,13,14,17,18,21,22,25,26,29,11,12,15,16,19,20,23, %T A249506 24,27,28,30,33,34,37,38,41,42,45,46,49,31,32,35,36,39,40,43,44,47,48, %U A249506 50,53,54,57,58,61,62,65,66,69,51,52,55,56,59,60,63,64,67,68,70,73,74,77,78,81,82,85 %N A249506 Inverse permutation to A249494 (= permutation of the positive integers such that the parity of the first digit of a(n+1) equals that of a(n)'s last digit). %C A249506 See A249278 and A249279 for the variant based on nonnegative integers; A162501 is a variant based not on parity but on equality. %H A249506 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %o A249506 (PARI) a=vector(#A249494);for(i=1,#a,A249494[i]<=#a&&a[A249494[i]]=i);a \\ Result only valid up to the first zero. %Y A249506 Cf. A000030, A162501. %K A249506 nonn %O A249506 1,2 %A A249506 _M. F. Hasler_, Oct 30 2014