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

1,1

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

Links

Table of n, a(n) for n=1..10.

Mathematica

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

Prog

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

Crossrefs

Cf. A000166, A000255.

Sequence in context: A076138 A050037 A113005 * A072623 A006144 A047429

Adjacent sequences: A301420 A301421 A301422 * A301424 A301425 A301426

Keyword

nonn,more

Author

Amiram Eldar, Mar 20 2018

Status

approved