OFFSET
1,1
COMMENTS
a(12) > 100000. - Dana Jacobsen, Oct 03 2015
a(12) > 1173095 using A057201. - Michael S. Branicky, Sep 07 2024
FORMULA
EXAMPLE
For p=3, 2^3+21=29; p=5, 2^5+21=53; p=7, 2^7+21=149.
MATHEMATICA
Select[Prime[Range[10000]], PrimeQ[(2^# + 21)] &] (* Vincenzo Librandi, Oct 04 2015 *)
PROG
(Magma) [p: p in PrimesUpTo(4000) | IsPrime(2^p+21) ];
(Perl) use ntheory ":all"; use Math::GMP qw/:constant/; forprimes { my $n = 2**$_+21; say if is_prime($n) } 20000; # Dana Jacobsen, Oct 03 2015
(PARI) is(n)=prime(n)&&prime(2^n+21) \\ Anders Hellström, Oct 03 2015
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Vincenzo Librandi, Mar 09 2010
EXTENSIONS
a(10)-a(11) from Dana Jacobsen, Oct 03 2015
STATUS
approved