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A099351
Numbers k such that 5*k! - 1 is prime.
10
3, 5, 8, 13, 20, 25, 51, 97, 101, 241, 266, 521, 1279, 1750, 2204, 2473, 4193, 5181, 10080
OFFSET
1,1
COMMENTS
a(15) > 1879. - Jinyuan Wang, Feb 04 2020
a(17) > 3500. - Michael S. Branicky, Mar 06 2021
EXAMPLE
k = 5 is here because 5*5! - 1 = 599 is prime.
MAPLE
for n from 0 to 1000 do if isprime(5*n! - 1) then print(n) end if end do;
MATHEMATICA
Select[Range[550], PrimeQ[5#!-1]&] (* Harvey P. Dale, Nov 27 2013 *)
PROG
(PARI) is(n)=ispseudoprime(5*n!-1) \\ Charles R Greathouse IV, Jun 13 2017
(Python)
from sympy import isprime
from math import factorial
print([k for k in range(300) if isprime(5*factorial(k) - 1)]) # Michael S. Branicky, Mar 05 2021
KEYWORD
nonn,more
AUTHOR
Brian Kell, Oct 12 2004
EXTENSIONS
a(13)-a(14) from Jinyuan Wang, Feb 04 2020
a(15)-a(16) from Michael S. Branicky, Mar 05 2021
a(17)-a(18) from Michael S. Branicky, Apr 03 2023
a(19) from Michael S. Branicky, Jul 12 2024
STATUS
approved