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 A123719 #7 Jun 02 2025 00:31:11 %S A123719 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,21,19,20,18,22,23,24,25, %T A123719 26,27,28,29,30,31,35,33,34,32,36,37,38,39,40,41,42,43,44,45,58,56,54, %U A123719 49,63,51,52,53,48,62,47,57,46,59,60,61,55,50,64,65,66,67,68,69,70,71 %N A123719 An involution of nonnegative integers: signature permutation of Catalan automorphism which is obtained with recursion schema RIBS from automorphism *A085161. %C A123719 Recursion schema RIBS is defined in A122200. Number of fixed points in range [A014137(n-1)..A014138(n-1)] of this permutation is given by INVERT transform of A001405, appropriately shifted. %H A123719 <a href="/index/Per#IntegerPermutationCatAuto">Index entries for signature-permutations of Catalan automorphisms</a> %o A123719 (Scheme function, constructive implementation of this automorphism acting on S-expressions:) (define *A123719 (RIBS *A085161)) %Y A123719 a(n) = A085160(A085163(n)). A085163(n) = A085159(a(n)). %K A123719 nonn %O A123719 0,3 %A A123719 _Antti Karttunen_, Oct 11 2006