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 A087260 #10 Oct 20 2019 22:44:16
%S A087260 4,8,4,16,20,24,4,32,4,40,4,48,52,56,20,64,68,72,4,80,84,88,4,96,100,
%T A087260 104,4,112,116,40,4,128,132,136,20,144,148,152,4,160,4,168,4,176,180,
%U A087260 184,4,192,196,200,4,208,212,8,4,224,228,232,4,240,244,8,4,256,260,264
%N A087260 a(n) = gcd(4n, A025586(4n)), greatest common divisor of 4n and largest value in 3x+1 iteration list started at 4n.
%t A087260 c[x_] := (1-Mod[x, 2])*(x/2)+Mod[x, 2]*(3*x+1)c[1]=1; fpl[x_] := Delete[FixedPointList[c, x], -1] Table[GCD[4*w, Max[fpl[4*w]]], {w, 1, 256}]
%Y A087260 Cf. A025586, A033496-A087261.
%K A087260 nonn
%O A087260 1,1
%A A087260 _Labos Elemer_, Sep 09 2003