This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A157352 Products (semiprimes) of two distinct safe primes. 9
 35, 55, 77, 115, 161, 235, 253, 295, 329, 413, 415, 517, 535, 581, 649, 749, 835, 895, 913, 1081, 1135, 1169, 1177, 1253, 1315, 1357, 1589, 1735, 1795, 1837, 1841, 1909, 1915, 1969, 2335, 2395, 2429, 2461, 2497, 2513, 2515, 2681, 2773, 2815, 2893, 2935 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 35=5*7; 5 and 7 are safe primes, 55=5*11; 5 and 11 are safe primes,... LINKS Michael De Vlieger, Table of n, a(n) for n = 1..10000 EXAMPLE a(1) = 35 since 35 = 5 * 7, and (5 - 1)/2 = 2 and (7 - 1)/2 = 3 are both prime, thus 5 and 7 are distinct safe primes. MATHEMATICA lst={}; Do[If[Plus@@Last/@FactorInteger[n]==2, a=Length[First/@FactorInteger[n]]; If[a==2, b=First/@FactorInteger[n]; c=b[[1]]; d=b[[2]]; If[PrimeQ[(c-1)/2]&&PrimeQ[(d-1)/2], AppendTo[lst, n]]]], {n, 7!}]; lst Select[Select[Range@ 3000, PrimeNu@ # == 2 &], Times @@ Map[If[PrimeQ[(# - 1)/2], #, 0] &, Map[First, FactorInteger@ #]] == # &] (* Michael De Vlieger, Feb 28 2016 *) Module[{upto=3000, sp}, sp=Select[Prime[Range[PrimePi[upto/5]]], PrimeQ[(#-1)/2]&]; Select[Union[Times@@@Subsets[sp, {2}]], #<+upto&]] (* Harvey P. Dale, Aug 25 2017 *) CROSSREFS Cf. A001358, A005384, A005385, A006881, A007304, A111206, A157342, A157344, A157345, A157346, A157347. Sequence in context: A121707 A267999 A319386 * A176255 A090877 A048033 Adjacent sequences:  A157349 A157350 A157351 * A157353 A157354 A157355 KEYWORD nonn AUTHOR Vladimir Joseph Stephan Orlovsky, Feb 27 2009 EXTENSIONS Example corrected by Harvey P. Dale, Aug 25 2017 STATUS approved

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

Last modified October 20 10:25 EDT 2019. Contains 328257 sequences. (Running on oeis4.)