A258616 Numbers n such that n!!-16 is prime.

7, 9, 13, 17, 25, 185, 197, 261, 407, 593, 1535, 2129, 2139, 2581, 4133, 4665, 15787, 25337, 27449

Offset: 1

Author

Robert Price, Jun 05 2015

Keywords

• hard
• more
• nonn

Comments

Corresponding primes are 89, 929, 135119, 34459409, ... .

a(20) > 50000.

Links

• Joe McLean, Interesting Sources of Probable Primes

Crossrefs

Cf. A006882, A007749, A094144, A123910.

Programs

Mathematica

Select[Range[4,1000],PrimeQ[#!!-16]&] (* Robert Price, Jun 05 2015 *)
Do[f=n!! - 16; If[PrimeQ[f], Print[{n, f}]], {n, 4, 600}] (* Vincenzo Librandi, Jun 06 2015 *) (see comment)