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A157342 Semiprimes that are the product of two non-Sophie Germain primes. 12
49, 91, 119, 133, 169, 217, 221, 247, 259, 289, 301, 323, 329, 361, 403, 413, 427, 469, 481, 497, 511, 527, 553, 559, 589, 611, 629, 679, 703, 707, 721, 731, 749, 763, 767, 793, 799, 817, 871, 889, 893, 923, 949, 959, 961, 973, 1003, 1027, 1037, 1043, 1057 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

49 = 7*7, 2*7 + 1 = 15 (not prime);

91 = 7*13, 2*7 + 1 = 15 (not prime), 2*13 + 1 = 27 (not prime); ...

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..5000

MATHEMATICA

lst={}; Do[If[Plus@@Last/@FactorInteger[n]==2, a=First/@FactorInteger[n]; b=a[[1]]; k=0; If[Length[a]==2, c=a[[2]]; If[PrimeQ[2*c+1], k=1]]; If[ !PrimeQ[2*b+1]&&k==0, AppendTo[lst, n]]], {n, 7!}]; lst

With[{nn=60}, Take[Times@@@Tuples[Select[Prime[Range[nn]], !PrimeQ[ 2#+1]&], 2] // Union, nn]] (* Harvey P. Dale, Feb 15 2017 *)

CROSSREFS

Cf. A001358, A005384, A111206.

Sequence in context: A231275 A158725 A090825 * A230226 A178705 A118886

Adjacent sequences:  A157339 A157340 A157341 * A157343 A157344 A157345

KEYWORD

nonn

AUTHOR

Vladimir Joseph Stephan Orlovsky, Feb 27 2009

STATUS

approved

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Last modified June 16 04:56 EDT 2021. Contains 345056 sequences. (Running on oeis4.)