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 A123499 #6 Mar 31 2012 13:21:12 %S A123499 0,1,3,2,6,7,8,5,4,14,15,16,17,18,19,20,21,12,13,22,11,9,10,37,38,39, %T A123499 40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,31,32,59,34, %U A123499 35,36,60,61,62,30,33,63,28,23,24,64,29,25,26,27,107,108,109,110,111 %N A123499 Signature permutation of a nonrecursive Catalan automorphism: rotate a binary tree left if possible, otherwise apply *A089863. %C A123499 This automorphism is illustrated below, where letters A, B and C refer to arbitrary subtrees located on those nodes and () stands for an implied terminal node. %C A123499 ...B...C...............A...B...........A...B.............B...A %C A123499 ....\./.................\./.............\./...............\./. %C A123499 .A...x........-->........x...C...........x..()...-->...()..x.. %C A123499 ..\./.....................\./.............\./...........\./... %C A123499 ...x.......................x...............x.............x.... %C A123499 (a . (b . c)) --> ((a . b) . c) / ((a . b) . ()) --> (() . (b . a)) %C A123499 This automorphism cannot be represented as a composition of two smaller nonrecursive automorphisms. Cf. A123503. %H A123499 A. Karttunen, <a href="/A089840/a089840p.txt">Prolog-program which illustrates the construction of this and other similar nonrecursive Catalan automorphisms.</a> %H A123499 <a href="/index/Per#IntegerPermutationCatAuto">Index entries for signature-permutations of Catalan automorphisms</a> %o A123499 (Scheme function, destructive implementation of this automorphism acting on S-expressions:) (define (*A123499! s) (cond ((null? s) s) ((pair? (cdr s)) (*A074679! s)) (else (*A089863! s))) s) %Y A123499 Inverse: A123500. Row 258 of A089840. Variant of A074679. %K A123499 nonn %O A123499 0,3 %A A123499 _Antti Karttunen_, Oct 11 2006