OFFSET
1,1
COMMENTS
It is convenient, although not necessary, to let k be an odd number since k even => 4^k + k is even > 2.
Conjecture: sequence is infinite.
The next term (a(8)) has 126 digits. - Harvey P. Dale, Jun 05 2014
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..9
FORMULA
EXAMPLE
For k = 3, 4^3 + 3 = 67 is prime.
MATHEMATICA
Select[Table[4^n+n, {n, 1, 251, 2}], PrimeQ] (* Harvey P. Dale, Jun 05 2014 *)
PROG
(PARI) f(n) = for(x=1, n, y=2^x+x; if(isprime(y), print1(y", ")))
CROSSREFS
KEYWORD
nonn
AUTHOR
Cino Hilliard, Jun 10 2007, Aug 20 2007
STATUS
approved