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 A325420 #11 May 09 2019 12:22:58
%S A325420 3,5,6,9,12,15,17,21,23,24,27,29,30,33,37,39,41,42,45,48,51,53,54,57,
%T A325420 60,63,65,66,69,71,73,75,77,78,81,84,87,89,93,95,96,99,101,102,105,
%U A325420 108,111,113,114,117,119,120,123,125,129,132,135,137,138,141,145
%N A325420 Complement of A325419.
%C A325420 These are the numbers 2x+1 and 3x as x ranges through the numbers in A325419.
%H A325420 Clark Kimberling, <a href="/A325420/b325420.txt">Table of n, a(n) for n = 1..10000</a>
%t A325420 a = {1}; Do[AppendTo[a, NestWhile[# + 1 &, Last[a] + 1, Apply[Or,
%t A325420 Map[MemberQ[a, #] &, Select[Flatten[{#/3, (# - 1)/2}],
%t A325420 IntegerQ]]] &]], {150}]; a; (* A325419 *)
%t A325420 Complement[Range[Last[a]], a]; (* A325420 *)
%t A325420 (* _Peter J. C. Moses_, Apr 23 2019 *)
%Y A325420 Cf. A325417, A325419.
%K A325420 nonn,easy
%O A325420 1,1
%A A325420 _Clark Kimberling_, Apr 28 2019