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 A257726 #25 Sep 13 2015 05:10:41 %S A257726 0,1,2,3,4,7,5,9,6,13,11,25,8,15,14,33,10,21,19,51,17,43,35,115,12,31, %T A257726 22,67,20,63,45,163,16,37,29,93,27,79,66,273,24,73,57,223,47,171,146, %U A257726 723,18,49,42,151,30,99,88,385,28,87,83,349,59,235,203,1093,23,69,50,193,40,135,119,559,38,129,102,475,86,367,335,1983,34,111 %N A257726 a(0)=0; a(2n) = unlucky(a(n)), a(2n+1) = lucky(a(n)+1), where lucky = A000959, unlucky = A050505. %C A257726 This sequence can be represented as a binary tree. Each left hand child is produced as A050505(n), and each right hand child as A000959(1+n), when a parent contains n >= 1: %C A257726 0 %C A257726 | %C A257726 ...................1................... %C A257726 2 3 %C A257726 4......../ \........7 5......../ \........9 %C A257726 / \ / \ / \ / \ %C A257726 / \ / \ / \ / \ %C A257726 / \ / \ / \ / \ %C A257726 6 13 11 25 8 15 14 33 %C A257726 10 21 19 51 17 43 35 115 12 31 22 67 20 63 45 163 %C A257726 etc. %C A257726 Because all lucky numbers are odd, it means that even terms can only occur in even positions (together with odd unlucky numbers, for each one of which there is a separate infinite cycle), while terms in odd positions are all odd. %H A257726 Antti Karttunen, <a href="/A257726/b257726.txt">Table of n, a(n) for n = 0..512</a> %H A257726 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %F A257726 a(0)=0; after which, a(2n) = A050505(a(n)), a(2n+1) = A000959(a(n)+1). %F A257726 As a composition of other permutations. For all n >= 1: %F A257726 a(n) = A257731(A246378(n)). %F A257726 a(n) = A257733(A237126(n)). %F A257726 a(n) = A257801(A257728(n)). %o A257726 (Scheme, with memoizing definec-macro) %o A257726 (definec (A257726 n) (cond ((zero? n) n) ((even? n) (A050505 (A257726 (/ n 2)))) (else (A000959 (+ 1 (A257726 (/ (- n 1) 2))))))) %Y A257726 Inverse: A257725. %Y A257726 Cf. A000959, A050505, A005408, A005843. %Y A257726 Related or similar permutations: A237126, A246378, A257728, A257731, A257733, A257801. %Y A257726 Cf. also A183089 (another similar permutation, but with a slightly different definition, resulting the first differing term at n=9, where a(9) = 13, while A183089(9) = 21). %Y A257726 Cf. also A257735 - A257738. %K A257726 nonn,tabf %O A257726 0,3 %A A257726 _Antti Karttunen_, May 06 2015