OFFSET
0,4
COMMENTS
See A225768 for motivation and references.
EXAMPLE
a(0) = 0 since k^8 is not prime for any k > 0.
a(4) = 1 since k^8 + 4 is prime for k = 1, although k^8 + 4 = (k^4 - 2k^2 + 2)(k^4 + 2k^2 + 2), but the first factor equals 1 for k = 1.
a(64) = 0 since k^8 + 64 = (k^4 - 4*k^2 + 8)(k^4 + 4k^2 + 8) which is composite for all integers k > 1.
PROG
(PARI) A225770(a, b=8)={#factor(x^b+a)~==1&for(n=1, 9e9, ispseudoprime(n^b+a)&return(n)); a==0 || a==64 || print1("/*"factor(x^b+a)"*/")} \\ For illustrative purpose only. The polynomial is factored to avoid an infinite search loop when it is composite. But a factored polynomial can yield a prime when all factors but one equal 1. This happens for n=4, cf. example.
CROSSREFS
KEYWORD
nonn
AUTHOR
M. F. Hasler, Jul 25 2013
STATUS
approved