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 A028398 #12 Nov 04 2013 12:40:24 %S A028398 0,1,2,4,8,14,40,44,64,80,82,104,136,172,184,188,242,256,274,280,296, %T A028398 352,368,382,386,424,472,496,526,530,608,622,638,640,652,670,688,692, %U A028398 712,716,752,760,782,784,800,814,824,832,860,878,904,910,932,964,980,1022 %N A028398 When map in A006368 is iterated, all numbers fall into cycles; order cycles by smallest entry; a(n) is smallest entry in n-th cycle (some cycles are infinite). %C A028398 Iterations of A006368 starting with a(3)=4, a(4)=8, a(5)=14 and a(6)=40 give trajectories A180853, A028393, A028395, A182205 respectively. [_Reinhard Zumkeller_, Apr 18 2012] %D A028398 D. Gale, Tracking the Automatic Ant and Other Mathematical Explorations, A Collection of Mathematical Entertainments Columns from The Mathematical Intelligencer, Springer, 1998; see p. 16. %H A028398 <a href="/index/3#3x1">Index entries for sequences related to 3x+1 (or Collatz) problem</a> %K A028398 nonn %O A028398 0,3 %A A028398 _J. H. Conway_ and _Wouter Meeussen_