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 A082984 #30 Jul 16 2021 01:40:55 %S A082984 1,2,3,5,6,7,9,11,14,15,18,19,27,31,41,47,54,55,62,63,71,73,82,83,91, %T A082984 94,95,97,108,109,110 %N A082984 Numbers k for which the 3x+1 problem takes at least k halving and tripling steps to reach 1. %C A082984 This sequence is almost certainly full; there are no more terms below 100000. %C A082984 An exhaustive search revealed no further results up to 10^9. - _Gonzalo Ciruelos_, Aug 02 2013 %C A082984 If we do not count the initial number, then 1 and 2 do not appear in this sequence. It appears that no number k has a Collatz iteration requiring more than 5*k iterations. - _T. D. Noe_, Feb 21 2014 %H A082984 Gonzalo Ciruelos, <a href="/A082984/a082984.py.txt">Python script to generate the sequence.</a> %H A082984 <a href="/index/3#3x1">Index entries for sequences related to 3x+1 (or Collatz) problem</a> %e A082984 3 is in the list because it takes A006577(3) = 7 steps to reach 1 (3 -> 10 -> 5 -> 16 -> 8 -> 4 -> 2 -> 1). %t A082984 Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; Select[Range[1000], Length[Collatz[#]] >= # &] (* _T. D. Noe_, Feb 21 2014 *) %Y A082984 Cf. A006577, A006666, A008908. %K A082984 nonn,hard,more %O A082984 1,2 %A A082984 Hauke Worpel (hw1(AT)email.com), May 29 2003