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 A123502 #5 Mar 31 2012 13:21:12 %S A123502 0,1,2,3,4,7,5,6,8,9,10,17,16,18,11,20,12,14,15,13,19,21,22,23,24,25, %T A123502 26,27,45,46,44,42,49,48,43,47,50,28,29,54,53,55,30,57,31,37,38,32,39, %U A123502 40,41,33,61,34,51,52,35,56,58,59,36,60,62,63,64,65,66,67,68,69,70,71 %N A123502 Signature permutation of a Catalan automorphism: first recurse into the left subtree of the right hand side subtree of a binary tree and after that apply *A123498 at the root. %H A123502 <a href="/index/Per#IntegerPermutationCatAuto">Index entries for signature-permutations of Catalan automorphisms</a> %o A123502 (Scheme function, destructive implementation of this automorphism acting on S-expressions:) (define (*A123502! s) (cond ((and (pair? s) (pair? (cdr s))) (*A123502! (cadr s)))) (*A123498! s) s) %Y A123502 Inverse: A123501. A057502(n) = A083927(a(A057123(n))) = A083927(A085160(A057123(n))). %K A123502 nonn %O A123502 0,3 %A A123502 _Antti Karttunen_, Oct 11 2006