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 A154449 #4 Mar 31 2012 13:21:17 %S A154449 0,1,2,3,5,4,6,7,8,12,13,11,9,10,15,14,16,17,18,19,20,21,22,32,31,34, %T A154449 35,36,30,33,28,23,24,29,25,26,27,40,41,39,37,38,43,42,44,45,46,47,48, %U A154449 49,50,52,51,53,54,55,56,57,58,59,60,61,62,63,64,91,92,90,87,88,97,96 %N A154449 Signature permutation of a Catalan bijection induced by generator "a" of the rightward recursing instance of Basilica group wreath recursion: a = (1,b), b = s(1,a). %C A154449 This automorphism of rooted plane binary trees switches the two descendant trees for every other vertex as it returns back toward the root, after descending down to the rightmost tip of the tree along the 111... ray, so that the last vertex whose descendants are swapped, is the right-hand side child of the root and the root itself is fixed. Specifically, *A154449 = psi(A154439), where the isomorphism psi is given in A153141 (see further comments there). %H A154449 A. Karttunen, <a href="/A154449/b154449.txt">Table of n, a(n) for n = 0..2055</a> %H A154449 <a href="/index/Per#IntegerPermutationCatAuto">Index entries for signature-permutations of Catalan automorphisms</a> %o A154449 (Scheme function, destructive implementation of this automorphism acting on S-expressions:) (define (*A154449! s) (if (pair? s) (*A154451! (cdr s))) s) %Y A154449 Inverse: A154450. a(n) = A154455(A069768(n)) = A057163(A154453(A057163(n))). Cf. A154451. %K A154449 nonn %O A154449 0,3 %A A154449 _Antti Karttunen_, Jan 17 2009