A157347 Products of 3 distinct non-Sophie Germain primes.

1547, 1729, 2261, 2821, 3367, 3689, 3913, 4123, 4199, 4277, 4403, 4921, 5117, 5369, 5551, 5593, 5719, 6097, 6251, 6461, 6643, 6851, 7021, 7189, 7259, 7657, 7847, 7973, 8029, 8113, 8177, 8449, 8687, 8827, 8911, 9139, 9191, 9331, 9373, 9401, 9443, 9503

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..5600

Example

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

Mathematica

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

Prog

(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

Crossrefs

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

Sequence in context: A246899 A090209 A283154 * A255356 A336221 A020408

Adjacent sequences: A157344 A157345 A157346 * A157348 A157349 A157350

Keyword

nonn

Author

Vladimir Joseph Stephan Orlovsky, Feb 27 2009

Extensions

Entries verified by Klaus Brockhaus, Apr 11 2009

Status

approved