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 A050124 #15 Oct 06 2019 02:56:35
%S A050124 1,2,4,8,16,3,6,12,24,48,9,18,36,7,14,28,5,10,20,40,80,160,32,64,128,
%T A050124 25,50,100,200,400,800,1600,320,640,1280,256,51,102,204,408,81,162,
%U A050124 324,648,129,258,516,103,206,41,82,164,328,65
%N A050124 a(1)=1; for n > 1, a(n) = floor(a(n-1)/5) if this is not among 0,a(1),...,a(n-1); otherwise a(n) = 2*a(n-1).
%H A050124 Ivan Neretin, <a href="/A050124/b050124.txt">Table of n, a(n) for n = 1..10000</a>
%t A050124 Rest@Nest[Append[#, If[FreeQ[#, r = Quotient[#[[-1]], 5]], r, 2 #[[-1]]]] &, {0, 1}, 53] (* _Ivan Neretin_, Jul 31 2016 *)
%Y A050124 Cf. A050000 and references therein.
%K A050124 nonn
%O A050124 1,2
%A A050124 _Clark Kimberling_