login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A309548 Numbers k such that sigma(k)! - 1 is prime, where sigma is A000203. 0
2, 3, 4, 5, 6, 11, 13, 21, 29, 31, 37, 170, 180, 214, 234, 265, 362, 369, 10734, 14318, 19679, 19876, 39636, 48784, 62517, 76225, 77277, 83629, 85519, 90649, 92287 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
2 is a term because sigma(2) = 3. 3! - 1 = 5, a prime.
6 is a term because sigma(6) = 12. 12! - 1 = 479001599, a prime.
PROG
(SageMath)
[n for n in range(1, 150) if is_prime(factorial(sigma(n))-1)]
(PARI) isok(n) = isprime(sigma(n)!-1); \\ Michel Marcus, Aug 07 2019
CROSSREFS
Sequence in context: A082657 A108378 A084588 * A088411 A075073 A157420
KEYWORD
nonn,more
AUTHOR
Hauke Löffler, Aug 07 2019
EXTENSIONS
a(12)-a(24) from Daniel Suteu, Aug 07 2019
a(25)-a(31) from Amiram Eldar, May 14 2023
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 24 10:07 EDT 2024. Contains 373674 sequences. (Running on oeis4.)