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
Keywords
Examples
7 + 1! = 8 is not prime. 7 + 2! = 9 is not prime. 7 + 3! = 13 is prime. Thus a(7) = 3.
Links
- Vaclav Kotesovec, Table of n, a(n) for n = 1..5000
Crossrefs
Cf. A245723.
Programs
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PARI
a(n)=for(k=1,n,if(ispseudoprime(n+k!),return(k))) vector(150,n,a(n))
Comments