OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..40 (terms 1..30 from Vincenzo Librandi)
FORMULA
EXAMPLE
2049 is a member because 2049 = 2^11+1 = 3*683.
MATHEMATICA
Select[Table[2^n + 1, {n, 100}], PrimeOmega[#] == 2&] (* Vincenzo Librandi, Sep 21 2012 *)
PROG
(Magma) IsSemiprime:=func<n | &+[d[2]: d in Factorization(n)] eq 2>; [s: n in [2..100] | IsSemiprime(s) where s is 2^n+1]; // Vincenzo Librandi, Sep 21 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov, Feb 27 2004
STATUS
approved