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 A207675 #20 Feb 16 2025 08:33:16
%S A207675 9,15,18,21,27,30,33,35,36,39,42,45,51,54,55,57,60,63,66,69,70,72,75,
%T A207675 77,78,81,84,85,87,90,91,93,95,96,99,102,105,108,110,111,114,115,117,
%U A207675 119,120,121,123,125,126,129,132,133,135,138,140,141,143,144,145
%N A207675 Numbers such that not all divisors occur in their Collatz trajectories.
%H A207675 Reinhard Zumkeller, <a href="/A207675/b207675.txt">Table of n, a(n) for n = 1..10000</a>
%H A207675 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CollatzProblem.html">Collatz Problem</a>
%H A207675 Wikipedia, <a href="http://en.wikipedia.org/wiki/Collatz_conjecture">Collatz conjecture</a>
%H A207675 <a href="/index/3#3x1">Index entries for sequences related to 3x+1 (or Collatz) problem</a>
%e A207675 3 is a divisor of 9, not occurring in A033479 - therefore 9 is a term.
%t A207675 coll[n_]:=NestWhileList[If[EvenQ[#],#/2,3#+1]&,n,#>1&]; Select[Range[145],Complement[Divisors[#],coll[#]]!={}&] (* _Jayanta Basu_, May 27 2013 *)
%o A207675 (Haskell)
%o A207675 import Data.List (intersect)
%o A207675 a207675 n = a207675_list !! (n-1)
%o A207675 a207675_list = filter
%o A207675 (\x -> a027750_row x `intersect` a070165_row x /= a027750_row x) [1..]
%Y A207675 Cf. A027750, A070165, A006370, A207674 (complement).
%K A207675 nonn
%O A207675 1,1
%A A207675 _Reinhard Zumkeller_, Feb 20 2012