A204660 Numbers n such that n!9+1 is prime.

0, 1, 2, 4, 6, 10, 11, 12, 13, 14, 16, 17, 18, 19, 21, 24, 25, 32, 40, 43, 48, 49, 50, 57, 60, 71, 73, 82, 83, 86, 97, 105, 114, 121, 142, 147, 159, 168, 195, 205, 210, 212, 233, 262, 288, 289, 300, 309, 316, 323, 356, 403, 447, 505, 514, 553, 735, 739, 777

Offset: 1

Author

M. F. Hasler, Jan 17 2012

Keywords

• nonn
• hard

Comments

n!9 = A114806(n).

a(107) > 50000. - Robert Price, Jun 18 2012

a(1)-a(106) verified prime by deterministic test of PFGW. - Robert Price, Jun 18 2012

Links

• Robert Price, Table of n, a(n) for n = 1..106
• Ken Davis, Status of Search for Multifactorial Primes.
• Ken Davis, Results for n!9+1.

Crossrefs

Cf. A204657, A204658, A204659, A204661, A204662, A204663, A204664, A156165, A156167, A085150, A085148, A085146, A037083, A080778, A002981.

Programs

Mathematica

MultiFactorial[n_, k_] := If[n < 1, 1, n*MultiFactorial[n - k, k]];
Select[Range[0, 1000], PrimeQ[MultiFactorial[#, 9] + 1] & ] (* Robert Price, Apr 19 2019 *)
Select[Range[0,800],PrimeQ[Times@@Range[#,1,-9]+1]&] (* Harvey P. Dale, Aug 19 2021 *)

PARI

for(n=0,9999,isprime(prod(i=0,(n-2)\9,n-9*i)+1)& print1(n","))