A245714 Least number k > 0 such that n + k! is prime, or 0 if no such k exists.

1, 1, 2, 1, 2, 1, 3, 0, 2, 1, 2, 1, 3, 0, 2, 1, 2, 1, 4, 0, 2, 1, 3, 0, 3, 0, 2, 1, 2, 1, 3, 0, 0, 0, 2, 1, 3, 0, 2, 1, 2, 1, 4, 0, 2, 1, 3, 0, 4, 0, 2, 1, 3, 0, 3, 0, 2, 1, 2, 1, 3, 0, 0, 0, 2, 1, 3, 0, 2, 1, 2, 1, 3, 0, 0, 0, 2, 1, 4, 0, 2, 1, 3, 0, 4, 0, 2, 1, 4, 0, 3, 0, 0, 0, 2, 1, 3, 0, 2, 1, 2, 1, 3, 0, 2, 1, 2, 1, 5, 0, 2, 1, 4, 0, 4, 0, 0, 0, 5

Offset

1,3

Comments

a(n) <= n for all n. Thus a(n) = 0 is definite.

Links

Vaclav Kotesovec, Table of n, a(n) for n = 1..5000

Example

7 + 1! = 8 is not prime.
7 + 2! = 9 is not prime.
7 + 3! = 13 is prime. Thus a(7) = 3.

Prog

(PARI)
a(n)=for(k=1, n, if(ispseudoprime(n+k!), return(k)))
vector(150, n, a(n))

Crossrefs

Cf. A245723.

Sequence in context: A113738 A287854 A355341 * A092953 A058574 A112165

Adjacent sequences: A245711 A245712 A245713 * A245715 A245716 A245717

Keyword

nonn

Author

Derek Orr, Jul 30 2014

Status

approved