A319224 Integers q for which f(q) = ((((q - 2)! - 1) / q) - 1) / (q + 1) is a prime number.

7, 11, 19, 61, 2557

Offset

1,1

Comments

For q < 7, f(q) is not an integer.

f(q) for q = 2557 is a PRP7592.

According to Wilson's theorem, f(q) can be an integer only if q is prime.

Links

Table of n, a(n) for n=1..5.

Mathematica

a[q_]:=If[PrimeQ[((((q - 2)! - 1) / q) - 1) / (q + 1)], q]; DeleteCases[Array[a, 100], Null] (* Stefano Spezia, Nov 04 2018 *)

Prog

(PARI) forprime(q=7, 2557, my(p = ((((q - 2)! - 1) / q) - 1) / (q + 1)); if(ispseudoprime(p), print1(q, ", ")))

Crossrefs

Cf. A193447, A319304.

Sequence in context: A307965 A323109 A023267 * A282037 A050562 A321806

Adjacent sequences: A319221 A319222 A319223 * A319225 A319226 A319227

Keyword

nonn,hard,more

Author

Rashid Naimi, Sep 13 2018

Status

approved