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 A133420 #13 Jan 15 2021 09:30:39 %S A133420 0,1,1,2,14,2,5,3,2,15,9,3,12,6,15,4,9,3,7,16,6,10,21,4,9,13,3,7,18, %T A133420 16,16,5,10,10,14,4,19,8,13,17,13,7,7,11,16,22,26,5,16,10,10,14,25,4, %U A133420 25,8,8,19,23,17,13,17,7,6,17,11,11,11,22,15,26,5,16,20,10,9,20,14,14,18,4,14 %N A133420 Number of steps to reach 1 under repeated applications of the "5x+1" map of A133419, or -1 if 1 is never reached. %C A133420 The 5x+1 map sends x to x/2 if x is even, x/3 if x is divisible by 3, otherwise 5x+1. %H A133420 R. J. Mathar, <a href="/A133420/b133420.txt">Table of n, a(n) for n = 1..20000</a> %H A133420 R. J. Mathar, <a href="/A133420/a133420.txt">Maple program to make b-file</a> %H A133420 Tomás Oliveira e Silva, <a href="http://sweet.ua.pt/tos/3x+1.html">The px+1 problem</a> %H A133420 <a href="/index/3#3x1">Index entries for sequences related to 3x+1 (or Collatz) problem</a> %Y A133420 Cf. A133419. %K A133420 nonn,easy %O A133420 1,4 %A A133420 _N. J. A. Sloane_, Nov 27 2007