A157347 - OEIS

%I #18 Feb 11 2022 17:24:37

%S 1547,1729,2261,2821,3367,3689,3913,4123,4199,4277,4403,4921,5117,

%T 5369,5551,5593,5719,6097,6251,6461,6643,6851,7021,7189,7259,7657,

%U 7847,7973,8029,8113,8177,8449,8687,8827,8911,9139,9191,9331,9373,9401,9443,9503

%N Products of 3 distinct non-Sophie Germain primes.

%H Vincenzo Librandi, <a href="/A157347/b157347.txt">Table of n, a(n) for n = 1..5600</a>

%e 1547 = 7*13*17 is a term: its prime factors 7, 13, and 17 are not Sophie Germain primes.

%t lst={};Do[If[Plus@@Last/@FactorInteger[n]==3,a=Length[First/@FactorInteger[n]];If[a==3,b=First/@FactorInteger[n];c=b[[1]];d=b[[2]];e=b[[3]];If[ !PrimeQ[2*c+1]&&!PrimeQ[2*d+1]&&!PrimeQ[2*e+1],AppendTo[lst,n]]]],{n,8!}];lst

%o (Magma) S:=[ p: p in PrimesUpTo(120) | not IsPrime(2*p+1) ]; T:=[ q: a, b, c in S | a lt b and b lt c and q lt 10000 where q is a*b*c ]; Sort(~T); T; // _Klaus Brockhaus_, Apr 11 2009

%Y Cf. A001358, A005384, A111206, A157342, A006881, A157344, A157345, A007304, A157346.

%K nonn

%O 1,1

%A _Vladimir Joseph Stephan Orlovsky_, Feb 27 2009

%E Entries verified by _Klaus Brockhaus_, Apr 11 2009