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 A162730 #15 Sep 18 2018 05:25:08
%S A162730 6,10,14,15,21,22,26,33,34,38,39,46,51,57,58,62,65,69,74,82,85,86,87,
%T A162730 91,93,94,106,111,118,122,123,129,133,134,141,142,145,146,158,159,166,
%U A162730 177,178,183,185,194,201,202,205,206,213,214,217,218,219,226,237,249,254
%N A162730 Semiprimes n = pq such that q = kp - k + 1, where p,q primes and k > 1.
%C A162730 It seems that most of the semiprimes of this form (but not all, only those satisfying an additional property) can be factored very quickly (e.g. numbers with up to 1200 decimal digits can be factored in a couple of seconds) using a very simple method.
%C A162730 Squarefree semiprimes n such that lpf(n)-1 divides n-1. Semiprimes n = pq with primes p < q such that p-1 divides q-1. If n is such a semiprime, then q^n == q (mod n). - _Thomas Ordowski_, Sep 18 2018
%o A162730 (PARI) isok(n) = {if ((bigomega(n) == 2) && (omega(n) == 2), my(p = factor(n)[1, 1], q = factor(n)[2, 1]); (q-1) % (p-1) == 0;);} \\ _Michel Marcus_, Sep 18 2018
%Y A162730 Subsequence of A006881 (squarefree semiprimes).
%K A162730 nonn
%O A162730 1,1
%A A162730 _Vassilis Papadimitriou_, Jul 12 2009, Jul 13 2009
%E A162730 More terms from _R. J. Mathar_, Aug 06 2009