%I A063640
%S A063640 13,19,29,31,43,53,67,71,79,103,131,139,149,173,191,223,239,269,283,
%T A063640 293,311,317,367,389,419,431,439,443,499,509,557,599,607,619,643,647,
%U A063640 653,659,683,743,773,787,797,823,827,907,947,971,1031,1039,1087,1091
%N A063640 Primes of form p*q*r + 1, where p, q and r are primes.
%C A063640 Also semiprimes of the form (p-1)/2 where p is a prime. - Robert G. Wilson 
               v Sep 01 2007.
%H A063640 Harry J. Smith, <a href="b063640.txt">Table of n, a(n) for n=1,...,1000</
               a>
%t A063640 Take[ Select[ Union@ Flatten@ Table[ Prime@p*Prime@q*Prime@r + 1, {p, 
               48}, {q, p}, {r, q}], PrimeQ@ # &], 53] (* Or *)
%t A063640 semiPrimeQ[x_] := Plus @@ Last /@ FactorInteger[x] == 2; Select[Prime@ 
               Range@ 182, semiPrimeQ[(# - 1)/2] &] (* Robert G. Wilson v (rgwv(AT)rgwv.com), 
               Sep 01 2007 *)
%o A063640 (PARI) { n=0; for (m=1, 10^9, p=prime(m); if (bigomega(p - 1) == 3, write("b063640.txt", 
               n++, " ", p); if (n==1000, break)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), 
               Aug 26 2009]
%Y A063640 Cf. A014612, A063639.
%Y A063640 Sequence in context: A109902 A058898 A123840 this_sequence A092104 A094105 
               A073620
%Y A063640 Adjacent sequences: A063637 A063638 A063639 this_sequence A063641 A063642 
               A063643
%K A063640 nonn
%O A063640 1,1
%A A063640 Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Jul 21 2001