A359180 Numbers k such that k!^2 / 2 + 1 is prime.

2, 3, 6, 18, 19, 82, 1298, 3139, 3687, 4637

Offset

1,1

Links

Table of n, a(n) for n=1..10.

Example

3!^2 / 2 + 1 = 6^2/2 + 1 = 19, a prime number, so 3 is a term.

Prog

(PARI) isok(k) = (k>1) && isprime(k!^2 / 2 + 1); \\ Michel Marcus, Jan 15 2023

Crossrefs

Cf. A002981, A046029, A358805, A358878.

Sequence in context: A169974 A003183 A213616 * A131788 A294455 A277703

Adjacent sequences: A359177 A359178 A359179 * A359181 A359182 A359183

Keyword

nonn,hard,more

Author

Arsen Vardanyan, Dec 18 2022

Extensions

a(7) from Michael S. Branicky, Dec 18 2022

a(8)-a(10) from Michael S. Branicky, Apr 10 2023

Status

approved