|
| |
|
|
A103317
|
|
Primes p such that p! - 1 is also prime.
|
|
5
|
| |
|
|
|
OFFSET
|
1,1
|
|
|
COMMENTS
|
The members are the primes in A002982 (n! - 1 is prime).
|
|
|
REFERENCES
|
R. K. Guy, Unsolved Problems in Number Theory, Section A2.
|
|
|
LINKS
|
Table of n, a(n) for n=1..5.
Eric Weisstein's World of Mathematics, Factorial Prime
Index entries for sequences related to factorial numbers.
|
|
|
EXAMPLE
|
3 is prime and 3! - 1 = 5 is prime, so 3 is a member.
|
|
|
MATHEMATICA
|
Select[Prime[Range[100]], PrimeQ[#! - 1] &] (* Vladimir Joseph Stephan Orlovsky, Feb 01 2012 *)
|
|
|
PROG
|
(PARI) isok(n) = ispseudoprime(n) && ispseudoprime(n!-1); \\ Jinyuan Wang, Jan 20 2020
|
|
|
CROSSREFS
|
Cf. A002982, A093804.
Sequence in context: A064774 A089689 A248701 * A104051 A128004 A281889
Adjacent sequences: A103314 A103315 A103316 * A103318 A103319 A103320
|
|
|
KEYWORD
|
nonn,hard,more
|
|
|
AUTHOR
|
Jonathan Sondow, Jan 31 2005
|
|
|
EXTENSIONS
|
a(5)=208003 (found on Jul 27 2016, by Sou Fukui), added by Jinyuan Wang, Jan 20 2020
|
|
|
STATUS
|
approved
|
| |
|
|
