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 A123498 #7 Mar 31 2012 13:21:12 %S A123498 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 A123498 26,27,45,46,44,42,43,48,47,49,50,28,29,54,53,55,30,57,31,37,38,32,39, %U A123498 40,41,33,61,34,51,52,35,56,58,59,36,60,62,63,64,65,66,67,68,69,70,71 %N A123498 Signature permutation of a nonrecursive Catalan automorphism: row 1654249 of table A089840. %H A123498 A. Karttunen, <a href="/A089840/a089840p.txt">Prolog-program which illustrates the construction of this and other similar nonrecursive Catalan automorphisms.</a> %H A123498 <a href="/index/Per#IntegerPermutationCatAuto">Index entries for signature-permutations of Catalan automorphisms</a> %o A123498 (Scheme function, destructive implementation of this automorphism acting on S-expressions:) (define (*A123498! s) (cond ((null? s) s) ((and (pair? (cdr s)) (pair? (cadr s))) (let ((old-cddr-s (cddr s))) (set-cdr! (cdr s) (cdadr s)) (set-cdr! (cadr s) old-cddr-s)) (*A074679! s)) ((pair? (cdr s)) (*A072796! s)) ((pair? (car s)) (*A072797! s))) s) %Y A123498 Inverse: A123497. Row 1654249 of A089840. Used to construct automorphism *A123502. A074679(n) = A083927(a(A057123(n))). %K A123498 nonn %O A123498 0,3 %A A123498 _Antti Karttunen_, Oct 11 2006