OFFSET
1,1
COMMENTS
a(40)>=206. - Amiram Eldar, Sep 29 2018
FORMULA
MATHEMATICA
k = {}; Do[If[ ! PrimeQ[2^Prime[n] - 1], c = FactorInteger[2^Prime[n] - 1]; d = Length[c]; If[d == 2, AppendTo[k, n]]], {n, 1, 40}]; k
Select[Range[40], PrimeNu[2^Prime[#]-1]==2&] (* Harvey P. Dale, Jul 07 2013 *)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Artur Jasinski, Dec 09 2007
EXTENSIONS
Edited by R. J. Mathar, May 03 2008
a(17)-a(34) from Donovan Johnson, Jun 14 2009
a(35)-a(39) from Amiram Eldar, Sep 29 2018
STATUS
approved