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 A162730 Semiprimes n = pq such that q = kp - k + 1, where p,q primes and k > 1. 2
 6, 10, 14, 15, 21, 22, 26, 33, 34, 38, 39, 46, 51, 57, 58, 62, 65, 69, 74, 82, 85, 86, 87, 91, 93, 94, 106, 111, 118, 122, 123, 129, 133, 134, 141, 142, 145, 146, 158, 159, 166, 177, 178, 183, 185, 194, 201, 202, 205, 206, 213, 214, 217, 218, 219, 226, 237, 249, 254 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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. 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 LINKS PROG (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 CROSSREFS Subsequence of A006881 (squarefree semiprimes). Sequence in context: A201650 A201514 A201464 * A180074 A338905 A093772 Adjacent sequences:  A162727 A162728 A162729 * A162731 A162732 A162733 KEYWORD nonn AUTHOR Vassilis Papadimitriou, Jul 12 2009, Jul 13 2009 EXTENSIONS More terms from R. J. Mathar, Aug 06 2009 STATUS approved

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Last modified May 8 18:28 EDT 2021. Contains 343666 sequences. (Running on oeis4.)