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 A354227 #21 Jul 18 2022 19:07:25
%S A354227 39,79,153,157,305,307,315,317,611,613,629,631,647,683,687,1221,1229,
%T A354227 1241,1257,1261,1265,1269,1295,1353,1367,1369,1375,1505,2445,2453,
%U A354227 2481,2483,2489,2507,2515,2517,2521,2525,2531,2545,2589,2593,2633,2705,2707,2733
%N A354227 Odd numbers whose Collatz trajectory contains exactly 12 odd numbers.
%F A354227 { A005408 } intersect { A072122 }.
%e A354227 305 is a term since its Collatz trajectory is 305, 916, 458, 229, 688, 344, 172, 86, 43, 130, 65, 196, 98, 49, 148, 74, 37, 112, 56, 28, 14, 7, 22, 11, 34, 17, 52, 26, 13, 40, 20, 10, 5, 16, 8, 4, 2, 1.
%t A354227 q[n_] := Count[NestWhileList[If[OddQ[#], 3 # + 1, #/2] &, n, # > 1 &], _?OddQ] == 12; Select[Range[1, 2750, 2], q] (* _Amiram Eldar_, May 20 2022 *)
%Y A354227 Cf. A005408, A072122.
%K A354227 nonn
%O A354227 1,1
%A A354227 _Krishna Kumar Arumugam_, May 20 2022