A240160 Least number k such that (k!-n)/k is prime, or 0 if no such k exists.

0, 0, 0, 4, 5, 0, 7, 8, 0, 0, 0, 4, 13, 0, 15, 4, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 31, 0, 33, 34, 5, 0, 0, 0, 39, 0, 0, 6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5, 6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 6, 0, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5

Offset: 1

Author

Derek Orr, Aug 01 2014

Keywords

• nonn

Comments

For a(n) > 0, a(n) is a divisor of n.

If a(n) = n, then n - 1 is in A002982.

Links

• Jens Kruse Andersen, Table of n, a(n) for n = 1..2500

Crossrefs

Cf. A002982, A240161, A245756.

Programs

PARI

a(n)=for(k=1,n,s=(k!-n)/k;if(floor(s)==s,if(ispseudoprime(s),return(k))))
vector(150, n, a(n))

Extensions

Typo in PARI code fixed by Colin Barker, Aug 02 2014