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 A271865 #13 Apr 19 2016 02:37:45 %S A271865 1,2,4,3,6,9,7,8,10,13,5,15,12,14,16,19,11,23,20,17,22,18,24,27,21,31, %T A271865 35,28,32,34,26,33,29,37,25,41,45,39,47,30,44,46,42,40,36,49,43,53,57, %U A271865 51,58,50,61,54,52,60,55,59,38,63,56,67,71,65,72,75,70 %N A271865 Recursive sequence based on the central polygonal numbers (A000124) and A004738. %C A271865 Conjectured to be a permutation of the natural numbers. %C A271865 The central polygonal numbers can be constructed by starting with the natural numbers, setting A000124(0)=1 and obtaining A000124(n+1) by reversing the order of the next A000124(n) numbers after A000124(n). This procedure doesn't produce a permutation of the natural numbers for A000124 because the sequence is strictly increasing. The present sequence is constructed by the same procedure, except that a(n+1) is obtained by reversing the next a(A004738(n)) numbers. %H A271865 Max Barrentine, <a href="/A271865/b271865.txt">Table of n, a(n) for n = 1..1124</a> %e A271865 Start with the natural numbers: %e A271865 1, 2, 3, 4, 5, 6, 7, 8, 9... %e A271865 a(A004738(1))=1, so reverse the order of the next term, leaving the sequence unchanged: %e A271865 (1) %e A271865 1, (2), 3, 4, 5, 6, 7, 8, 9... %e A271865 a(A004738(2))=2, so reverse the order of the next 2 terms: %e A271865 (2) %e A271865 1, 2, (4, 3), 5, 6, 7, 8, 9... %e A271865 a(A004738(3))=1, so reverse the order of the next term, leaving the sequence unchanged: %e A271865 (1) %e A271865 1, 2, 4, (3), 5, 6, 7, 8, 9... %e A271865 a(A004738(4))=2, so reverse the order of the next 2 terms: %e A271865 (2) %e A271865 1, 2, 4, 3, (6, 5), 7, 8, 9... %e A271865 a(A004738(5))=4, so reverse the order of the next 4 terms: %e A271865 (4) %e A271865 1, 2, 4, 3, 6, (9, 8, 7, 5)... %e A271865 a(A004738(6))=2, so reverse the order of the next 2 terms: %e A271865 (2) %e A271865 1, 2, 4, 3, 6, 9, (7, 8), 5... %e A271865 a(A004738(7))=1, so reverse the order of the next term, leaving the sequence unchanged: %e A271865 (1) %e A271865 1, 2, 4, 3, 6, 9, 7, (8), 5... %Y A271865 Cf. A000124, A004738. %K A271865 nonn %O A271865 1,2 %A A271865 _Max Barrentine_, Apr 16 2016