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 A272638 #8 Jul 11 2016 00:31:26 %S A272638 1,4,5,1,6,7,13,5,2,7,1,2,3,5,2,7,1,2,3,5,2,7,1,2,3,5,2,7,1,2,3,5,2,7, %T A272638 1,2,3,5,2,7,1,2,3,5,2,7,1,2,3,5,2,7,1,2,3,5,2,7,1,2,3,5,2,7,1,2,3,5, %U A272638 2,7,1,2,3,5,2,7,1,2,3,5,2,7,1,2,3,5,2,7 %N A272638 a(1)=1, a(2)=4; thereafter a(n) = squarefree part of a(n-1)+a(n-2). %p A272638 sqrf:= n-> mul(i[1]^irem(i[2], 2), i=ifactors(n)[2]): %p A272638 f:=proc(n) global sqrf; option remember; %p A272638 if n = 1 then 1 elif n=2 then 4 else sqrf(f(n-1)+f(n-2)); fi; end; %p A272638 [seq(f(n),n=1..140)]; %Y A272638 Rapidly merges with A272636. %Y A272638 Cf. A000045, A007913. %K A272638 nonn %O A272638 1,2 %A A272638 _N. J. A. Sloane_, May 05 2016