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 A154124 #5 Mar 31 2012 13:21:17 %S A154124 0,1,2,3,6,4,5,7,8,16,19,9,10,11,15,14,12,17,18,13,20,21,22,44,47,53, %T A154124 56,60,23,24,25,26,27,28,29,30,33,43,52,37,38,39,40,42,31,45,46,32,48, %U A154124 49,50,41,51,34,54,55,35,57,58,59,36,61,62,63,64,128,131,137,140,144 %N A154124 Signature permutation of a Catalan bijection: row 3748 of A089840. %C A154124 This bijection of binary trees is obtained in the following way. (Inverse of Thompson's B!): %C A154124 .B...C...............C...D %C A154124 ..\./.................\./ %C A154124 ...x...D....-->....B...x.................()..C ........A...() %C A154124 ....\./.............\./...................\./....-->....\./... %C A154124 .A...x...........A...x.................A...x.........C...x.... %C A154124 ..\./.............\./...................\./...........\./..... %C A154124 ...x...............x.....................x.............x...... %C A154124 .............................................................. %C A154124 That is, (a . ((b . c) . d)) -> (a . (b . (c . d))) %C A154124 or (a . (() . c)) -> (c . (a . ())) if the former is not possible. %H A154124 A. Karttunen, <a href="/A154124/b154124.txt">Table of n, a(n) for n = 0..2055</a> %H A154124 <a href="/index/Per#IntegerPermutationCatAuto">Index entries for signature-permutations of Catalan automorphisms</a> %o A154124 (Destructive version of this automorphism in Scheme:) (define (*A154124! s) (if (and (pair? s) (pair? (cdr s)) (pair? (cadr s))) (*A074680! (cdr s)) (*A089853! s)) s) %Y A154124 Inverse: A154123. Cf. A154122. %K A154124 nonn %O A154124 0,3 %A A154124 _Antti Karttunen_, Jan 06 2009