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 A213199 #26 May 15 2024 09:07:42 %S A213199 3,5,6,7,9,10,11,12,13,14,15,17,18,19,21,22,23,25,26,27,28,29,30,31, %T A213199 33,34,35,36,37,38,39,41,42,43,44,45,46,47,49,50,51,53,54,55,57,58,59, %U A213199 60,61,62,63,65,66,67,69,70,71,73,74,75,76,77,78,79,81,82,83 %N A213199 Numbers k whose Collatz (3x+1) trajectory includes at least one term that is greater than k. %H A213199 T. D. Noe, <a href="/A213199/b213199.txt">Table of n, a(n) for n = 1..1000</a> %e A213199 a(1) = 3 because 3 is the first number k whose trajectory goes above k. %t A213199 Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; Select[Range[100], Max[Collatz[#]] > # &] (* _T. D. Noe_, Mar 01 2013 *) %Y A213199 Cf. A033496, A222562, A222597. %K A213199 nonn %O A213199 1,1 %A A213199 _Jayanta Basu_, Mar 01 2013