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 A113981 #9 Apr 09 2014 10:16:40 %S A113981 1,2,4,3,6,5,8,7,10,9,12,11,14,13,16,15,18,17,20,19,23,24,21,22,26,25, %T A113981 28,27,30,29,32,31,36,37,40,33,34,41,42,35,38,39,44,43,46,45,48,47,50, %U A113981 49,52,51,54,53,56,55,59,60,57,58,62,61,64,63,66,65,68,67,70,69,72,71 %N A113981 a(1)=1. a(n) is smallest positive integer that does not occur earlier in the sequence and is such that d(a(n)) does not equal d(a(n-1)), where d(n) is the number of positive divisors of n. %C A113981 Sequence is a permutation of the positive integers. %H A113981 Diana Mecum, <a href="/A113981/b113981.txt">Table of n, a(n) for n = 1..1195</a> [From _Diana L. Mecum_, Aug 15 2008] %e A113981 Since d(a(4)) = d(3) = 2, d(a(5)) cannot be 2. a(5)= 6 is the smallest positive integer not occurring earlier in the sequence where d(a(5)) is not 2, since d(6) = 4. %Y A113981 Cf. A113982. %K A113981 nonn %O A113981 1,2 %A A113981 _Leroy Quet_, Nov 11 2005 %E A113981 More terms from _Diana L. Mecum_, May 29 2007 %E A113981 More terms from _Diana L. Mecum_, Aug 15 2008