OFFSET
1,2
COMMENTS
It is conjectured that there are infinitely many primes of the form x^4 + 1 (and thus this sequence never becomes constant), but this has not been proved.
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..46
EXAMPLE
a(3) = 3 because the only primes of the form x^4 + 1 < 10^3 are the primes: 2, 17, 257.
PROG
(PARI) a(n) = sum(k=1, (10^n-1)^(1/4), isprime(k^4+1))
CROSSREFS
KEYWORD
nonn
AUTHOR
Henryk Dabrowski, Jul 18 2012
EXTENSIONS
More terms from Henryk Dabrowski, Jul 26 2012
a(37)-a(40) from Chai Wah Wu, Oct 13 2018
STATUS
approved