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 A154454 #4 Mar 31 2012 13:21:17 %S A154454 0,1,2,3,4,5,6,8,7,9,10,11,12,13,14,15,19,21,22,16,20,17,18,23,24,25, %T A154454 26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,51,52,56,58,59,60,62, %U A154454 64,63,42,43,53,57,61,44,54,45,46,47,55,48,49,50,65,66,67,68,69,70,71 %N A154454 Signature permutation of a Catalan bijection: The inverse of A154453. %C A154454 This automorphism of rooted plane binary trees switches the two descendant trees for every other vertex as it descends along the 000... ray, but not starting swapping until at the left-hand side child of the root, leaving the root itself fixed. Specifically, *A154454 = psi(A154444), where the isomorphism psi is given in A153141 (see further comments there). %H A154454 A. Karttunen, <a href="/A154454/b154454.txt">Table of n, a(n) for n = 0..2055</a> %H A154454 <a href="/index/Per#IntegerPermutationCatAuto">Index entries for signature-permutations of Catalan automorphisms</a> %o A154454 (Scheme function, destructive implementation of this automorphism acting on S-expressions:) (define (*A154454! s) (if (pair? s) (*A154456! (car s))) s) %Y A154454 Inverse: A154453. a(n) = A069768(A154452(n)) = A057163(A154450(A057163(n))). Cf. A069770, A154456. %Y A154454 Differs from its inverse A154453 for the first time at n=49, where a(49)=64, while A154454(49)=63. Differs from A089854 for the first time at n=49, where a(49)=64, while A089854(49)=63. Differs from A131173 for the first time at n=26, where a(26)=26, while A131173(26)=27. %K A154454 nonn %O A154454 0,3 %A A154454 _Antti Karttunen_, Jan 17 2009