Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #10 Oct 20 2019 22:44:16
%S 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 104,4,112,116,40,4,128,132,136,20,144,148,152,4,160,4,168,4,176,180,
%U 184,4,192,196,200,4,208,212,8,4,224,228,232,4,240,244,8,4,256,260,264
%N a(n) = gcd(4n, A025586(4n)), greatest common divisor of 4n and largest value in 3x+1 iteration list started at 4n.
%t 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 Cf. A025586, A033496-A087261.
%K nonn
%O 1,1
%A _Labos Elemer_, Sep 09 2003