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 A050080 #12 Oct 05 2019 11:26:47
%S A050080 1,4,16,5,20,6,2,8,32,10,3,12,48,192,64,21,7,28,9,36,144,576,2304,768,
%T A050080 256,85,340,113,37,148,49,196,65,260,86,344,114,38,152,50,200,66,22,
%U A050080 88,29,116,464,154,51,17,68,272,90,30,120,40,13
%N A050080 a(n) = floor(a(n-1)/3) if this is not among 0, a(1), ..., a(n-2); otherwise a(n) = 4*a(n-1).
%H A050080 Ivan Neretin, <a href="/A050080/b050080.txt">Table of n, a(n) for n = 1..10000</a>
%t A050080 Rest@Nest[Append[#, If[FreeQ[#, r = Quotient[#[[-1]], 3]], r, 4 #[[-1]]]] &, {0, 1}, 56] (* _Ivan Neretin_, Jul 31 2016 *)
%Y A050080 Cf. A050000 and references therein.
%K A050080 nonn
%O A050080 1,2
%A A050080 _Clark Kimberling_