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A245714
Least number k > 0 such that n + k! is prime, or 0 if no such k exists.
4
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
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
KEYWORD
nonn
AUTHOR
Derek Orr, Jul 30 2014
STATUS
approved