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 A075378 #5 Dec 05 2013 19:55:37 %S A075378 1,2,4,3,8,5,9,6,12,7,16,10,18,11,20,13,24,14,25,15,27,17,28,19,32,21, %T A075378 36,22,40,23,44,26,45,29,48,30,49,31,50,33,52,34,54,35,56,37,60,38,63, %U A075378 39,64,41,68,42,72,43,75,46,76,47,80,51,81,53,84,55,88,57,90,58,92,59 %N A075378 Rearrangement of natural numbers with a(1) = 1, a(2n) squarefree and a(2n+1) not squarefree. %o A075378 (PARI) print1(1,",");p1=2;p2=4;for(i=2,100,if(i%2==0, while(!issquarefree(p1),p1++);print1(p1,",");p1++, while(issquarefree(p2),p2++);print1(p2,",");p2++)) - Lambert Herrgesell (zero815(AT)googlemail.com), Mar 09 2006 %K A075378 nonn %O A075378 1,2 %A A075378 _Amarnath Murthy_, Sep 22 2002 %E A075378 More terms from Lambert Herrgesell (zero815(AT)googlemail.com), Mar 09 2006