A301423 Numbers k such that !k/(k-1) is prime, where !k = A000166(k) is the subfactorial of k.

4, 5, 6, 11, 15, 44, 66, 168, 575, 1713

Offset: 1

Author

Amiram Eldar, Mar 20 2018

Keywords

• nonn
• more

Comments

Also numbers k such that A000255(k-2) is prime.

The corresponding primes are 3, 11, 53, 1468457, 34361893981, 22742406079421034331584846001936724930824184898296683, ...

a(11) > 35000. - Robert Price, Apr 14 2018

Crossrefs

Cf. A000166, A000255.

Programs

Mathematica

Select[Range[2,100], PrimeQ[Subfactorial[#]/(#-1)] &]

PARI

isok(n) = (n != 1) && isprime(n!*sum(k=0, n, (-1)^k/k!)/(n-1)); \\ Michel Marcus, Mar 24 2018