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 A069771 #7 Jan 13 2013 06:14:38 %S A069771 0,1,2,3,7,5,6,4,8,9,14,21,18,13,10,15,20,17,12,19,16,11,22,45,54,31, %T A069771 26,40,44,53,30,25,39,63,59,50,36,46,55,32,27,41,42,51,28,23,37,62,58, %U A069771 49,35,43,52,29,24,38,61,57,48,34,60,56,47,33,64,65,79,107,121,149,170 %N A069771 Self-inverse permutation of natural numbers induced by the automorphism RotateHandshakes180 acting on the parenthesizations encoded by A014486. %C A069771 This automorphism rotates by 180 degrees the interpretation n (the non-crossing handshakes) of Stanley's exercise 19. %H A069771 A. Karttunen, <a href="http://www.iki.fi/~kartturi/matikka/Nekomorphisms/gatomorf.htm">Gatomorphisms</a> (Includes the complete Scheme program for computing this sequence) %H A069771 R. P. Stanley, <a href="http://www-math.mit.edu/~rstan/ec/catalan.pdf">Exercises on Catalan and Related Numbers</a> %H A069771 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %o A069771 (Scheme function implementing this automorphism on list-structures:) (define (RotateHandshakes180 a) (RotateHandshakes_n_steps a (count-pars a))) %o A069771 (define (count-pars a) (if (not (pair? a)) 0 (+ 1 (count-pars (car a)) (count-pars (cdr a))))) %o A069771 (define (RotateHandshakes a) (if (null? a) (list) (append (car a) (list (cdr a))))) %o A069771 (define (RotateHandshakes_n_steps a n) (if (zero? n) a (RotateHandshakes_n_steps (RotateHandshakes a) (-1+ n)))) %Y A069771 Cf. A057501, A069772, A069888, A069889. %K A069771 nonn %O A069771 0,3 %A A069771 Antti Karttunen, Apr 16 2002