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 A179371 #2 Mar 31 2012 14:41:48 %S A179371 1,4,6,8,2,9,3,10,12,14,5,16,15,7,18,21,11,22,20,13,24,17,25,19,26,23, %T A179371 27,29,28,30,32,31,33,36,34,37,40,35,41,38,42,39,43,46,44,47,45,48,50, %U A179371 49,51,53,52,54,59,55,60,56,61,63,57,64,66,58,68,67,62,70,65,71,69,72 %N A179371 a(1) = 1; a(n) = smallest positive integer not already used which has a prime signature different from both a(n-1) and a(n-1)+1. %e A179371 To compute a(2), we see a(1) is 1; we look for the smallest unused positive integer that does not have the same prime signature as either 1 or 2. The first such number is 4. %Y A179371 Cf. A179372 %K A179371 nonn %O A179371 1,2 %A A179371 _Will Nicholes_, Jul 11 2010