A225769 Least k>0 such that k^7+n is prime, or 0 if there is no such k.

0, 1, 1, 2, 1, 6, 1, 16, 9, 2, 1, 2, 1, 6, 5, 22, 1, 8, 1, 10, 3, 2, 1, 2, 17, 12, 3, 4, 1, 2, 1, 6, 5, 4, 3, 2, 1, 4, 5, 2, 1, 6, 1, 4, 23, 2, 1, 24, 5, 4, 3, 2, 1, 2, 5, 6, 3, 28, 1, 8, 1, 22, 39, 2, 3, 2, 1, 4, 5, 2, 1, 2, 1, 6, 9, 34, 7, 6, 1, 10, 3, 16, 1, 2, 23, 22, 3, 14, 1, 14, 23, 12, 9, 4, 3, 2, 1, 4, 9, 2, 1, 2, 1, 4, 5, 2, 1, 8, 1, 4, 3, 2, 1, 2, 23, 12, 5, 40, 31, 92, 7

Offset

0,4

Comments

See A225768 for motivation and references.

Links

Table of n, a(n) for n=0..120.

Prog

(PARI) (a, b=5)->{#factor(x^b+a)~==1&for(n=1, 9e9, ispseudoprime(n^b+a)&return(n)); a==1 || 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 b=4, n=4, cf. A225766.

Crossrefs

See A085099, A225765--A225770 for the k^2, k^3, ..., k^8 analogs.

Sequence in context: A109193 A322672 A363595 * A280736 A279095 A186283

Adjacent sequences: A225766 A225767 A225768 * A225770 A225771 A225772

Keyword

nonn

Author

M. F. Hasler, Jul 25 2013

Status

approved