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 A372810 #16 May 25 2024 14:42:45 %S A372810 1,1,3,1,3,6,7,3,9,3,7,12,7,9,15,3,7,18,19,7,21,7,15,24,25,7,27,9,19, %T A372810 30,27,21,33,7,15,36,37,25,39,7,27,42,43,19,45,15,27,48,43,33,51,7,15, %U A372810 54,55,37,57,19,39,60,27,27,63,21,43,66,39,45,69,15,27 %N A372810 a(n) is the smallest number whose Collatz trajectory contains n, if trajectories do not terminate at 1 but continue to cycle through 1, 4, 2, 1, 4, 2, 1, ... . %C A372810 a(n) = A070167(n) for n >= 5. %C A372810 a(n) = n if 3 divides n. %D A372810 R. K. Guy, Unsolved Problems in Number Theory, E16. %H A372810 <a href="/index/3#3x1">Index entries for sequences related to 3x+1 (or Collatz) problem</a> %e A372810 For n=8, %e A372810 the trajectory of 1 is 1, 4, 2, 1, 4, ... (8 does not appear), and %e A372810 the trajectory of 2 is 2, 1, 4, 2, 1, ... (8 does not appear), but %e A372810 the trajectory of 3 is 3, 10, 5, 16, 8, ... (8 does appear), %e A372810 so a(8) = 3. %Y A372810 Cf. A070167 (sequence resulting if trajectories terminate at 1). %K A372810 nonn %O A372810 1,3 %A A372810 _Ethan E. Wood_, May 13 2024 %E A372810 Edited by _Jon E. Schoenfield_, May 13 2024