%I #33 Jul 12 2024 19:58:59

%S 3,5,8,13,20,25,51,97,101,241,266,521,1279,1750,2204,2473,4193,5181,

%T 10080

%N Numbers k such that 5*k! - 1 is prime.

%C a(15) > 1879. - _Jinyuan Wang_, Feb 04 2020

%C a(17) > 3500. - _Michael S. Branicky_, Mar 06 2021

%H <a href="/index/Pri#primepop">Index entries for sequences related to numbers of primes of the form k*n!+-1</a>

%e k = 5 is here because 5*5! - 1 = 599 is prime.

%p for n from 0 to 1000 do if isprime(5*n! - 1) then print(n) end if end do;

%t Select[Range[550],PrimeQ[5#!-1]&] (* _Harvey P. Dale_, Nov 27 2013 *)

%o (PARI) is(n)=ispseudoprime(5*n!-1) \\ _Charles R Greathouse IV_, Jun 13 2017

%o (Python)

%o from sympy import isprime

%o from math import factorial

%o print([k for k in range(300) if isprime(5*factorial(k) - 1)]) # _Michael S. Branicky_, Mar 05 2021

%Y Cf. A002982, A076133, A076134, A099350, A180627, A180628, A180629, A180630, A180631.

%K nonn,more

%O 1,1

%A _Brian Kell_, Oct 12 2004

%E a(13)-a(14) from _Jinyuan Wang_, Feb 04 2020

%E a(15)-a(16) from _Michael S. Branicky_, Mar 05 2021

%E a(17)-a(18) from _Michael S. Branicky_, Apr 03 2023

%E a(19) from _Michael S. Branicky_, Jul 12 2024