

A215699


Number of primes of the form 1 + b^512 for 1 < b < 10^n.


4




OFFSET

1,4


COMMENTS

Primes 1 + b^512 are a form of generalized Fermat primes.
It is conjectured that a(n) is asymptotic to 0.0146271*li(10^n)


LINKS



EXAMPLE

a(3) = 1 because the generalized Fermat numbers F_9(b) where b<10^3 are prime only for b = 46.


PROG

(PARI) a(n) = sum(b=1, 10^n/21, isprime((2*b)^512+1))


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



