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A129963
Primes of the form 4^k + k.
3
5, 67, 262153, 1073741839, 18889465931478580854821, 1496577676626844588240573268701473812127674924007509, 118571099379011784113736688648896417641748464297615937576404566024103044751294597
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
FORMULA
a(n) = A158879(A057909(n)). - Amiram Eldar, Jul 04 2024
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
Sequence in context: A197776 A197606 A207979 * A115764 A252794 A328359
KEYWORD
nonn
AUTHOR
Cino Hilliard, Jun 10 2007, Aug 20 2007
STATUS
approved