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 A087255 #11 Dec 02 2013 01:01:04 %S A087255 1,1,0,1,0,0,0,1,0,0,0,0,0,0,0,6,0,0,0,1,0,0,0,1,0,0,0,0,0,0,0,1,0,0, %T A087255 0,0,0,0,0,3,0,0,0,0,0,0,0,1,0,0,0,12,0,0,0,1,0,0,0,0,0,0,0,3,0,0,0,1, %U A087255 0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,1,0,0,0,8,0,0,0,0,0,0,0,1,0,0,0,3,0,0,0,1,0 %N A087255 Number of different initial values for 3x+1 trajectories of which the largest term appearing during the iteration equals n. %H A087255 Jon E. Schoenfield, <a href="/A087255/b087255.txt">Table of n, a(n) for n = 1..10000</a> %e A087255 a(2k+1)=a(4k+2)=a(16k+12)=0 because larger values appear in iteration: 6k+4, 6k+4, and 18k+16, respectively. Exception: a(1)=a(2)=1. %e A087255 Some outstanding cases: a(9232)=1579, a(13120)=75. %Y A087255 Cf. A025586, A087251-A087254. %K A087255 nonn %O A087255 1,16 %A A087255 _Labos Elemer_, Sep 08 2003 %E A087255 Edited by _Jon E. Schoenfield_, Dec 01 2013