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 A271861 #15 Apr 19 2016 02:33:13 %S A271861 1,2,3,5,4,7,9,8,10,12,15,14,6,16,19,11,13,18,21,24,20,28,27,25,22,30, %T A271861 23,34,37,36,26,29,33,17,41,44,40,39,32,35,45,31,49,52,48,55,54,51,38, %U A271861 46,50,58,61,57,64,67,66,56,43,59,47,68,71,63,74,77,81 %N A271861 Recursive sequence based on the central polygonal numbers (A000124) and A002260. %C A271861 Conjectured to be a permutation of the natural numbers. %C A271861 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(A002260(n)) numbers. %H A271861 Max Barrentine, <a href="/A271861/b271861.txt">Table of n, a(n) for n = 1..1227</a> %e A271861 Start with the natural numbers: %e A271861 1, 2, 3, 4, 5, 6, 7, 8, 9... %e A271861 a(A002260(1))=1, so reverse the order of the next term, leaving the sequence unchanged: %e A271861 (1) %e A271861 1, (2), 3, 4, 5, 6, 7, 8, 9... %e A271861 a(A002260(2))=1, so reverse the order of the next term, leaving the sequence unchanged: %e A271861 (1) %e A271861 1, 2, (3), 4, 5, 6, 7, 8, 9... %e A271861 a(A002260(3))=2, so reverse the order of the next 2 terms: %e A271861 (2) %e A271861 1, 2, 3, (5, 4), 6, 7, 8, 9... %e A271861 a(A002260(4))=1, so reverse the order of the next term, leaving the sequence unchanged: %e A271861 (1) %e A271861 1, 2, 3, 5, (4), 6, 7, 8, 9... %e A271861 a(A002260(5))=2, so reverse the order of the next 2 terms: %e A271861 (2) %e A271861 1, 2, 3, 5, 4, (7, 6), 8, 9... %e A271861 a(A002260(6))=3, so reverse the order of the next 3 terms: %e A271861 (3) %e A271861 1, 2, 3, 5, 4, 7, (9, 8, 6)... %Y A271861 Cf. A000124, A002260. %K A271861 nonn %O A271861 1,2 %A A271861 _Max Barrentine_, Apr 15 2016