The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A157342 Semiprimes that are the product of two non-Sophie Germain primes. 13
 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 LINKS G. C. Greubel, Table of n, a(n) for n = 1..5000 EXAMPLE 49 = 7*7, 2*7 + 1 = 15 (not prime); 91 = 7*13, 2*7 + 1 = 15 (not prime), 2*13 + 1 = 27 (not prime); ... 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: A158725 A090825 A350704 * A230226 A178705 A118886 Adjacent sequences: A157339 A157340 A157341 * A157343 A157344 A157345 KEYWORD nonn AUTHOR Vladimir Joseph Stephan Orlovsky, Feb 27 2009 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 4 01:40 EDT 2024. Contains 374905 sequences. (Running on oeis4.)