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 A174240 #16 Feb 24 2021 03:55:01
%S A174240 4,6,10,12,12,8,20,18,12,22,30,8,28,12,10,36,36,44,24,20,14,18,46,60,
%T A174240 28,20,52,33,58,60,36,40,66,84,20,90,70,28,15,18,24,92,78,36,82,110,
%U A174240 36,52,22,60,48,116,132,42,100,60,102,140,106,72,36,69,132,28
%N A174240 The multiplicative order of 2 mod n, where n an odd squarefree semiprime (A046388).
%H A174240 Vassilis Papadimitriou, <a href="/A174240/b174240.txt">Table of n, a(n) for n = 1..10000</a>.
%F A174240 a(n) = A002326((A046388(n)+1)/2). - _Amiram Eldar_, Feb 24 2021
%e A174240 For n = 1, a(1) = 4 is the multiplicative order of 2 mod 15 (15 is the first odd squarefree semiprime).
%t A174240 MultiplicativeOrder[2, #] & /@ Select[Range[1, 350, 2], PrimeOmega[#] == 2 && PrimeNu[#] == 2 &] (* _Amiram Eldar_, Feb 24 2021 *)
%o A174240 (PARI) lista(nn) = {forstep(n=1, nn, 2, if ((bigomega(n) == 2) && (omega(n)==2), print1(znorder(Mod(2, n)), ", ")););} \\ _Michel Marcus_, Feb 05 2015
%Y A174240 Cf. A002326, A046388.
%K A174240 nonn
%O A174240 1,1
%A A174240 _Vassilis Papadimitriou_, Mar 13 2010
%E A174240 Edited by _Ray Chandler_, Jan 09 2012