A239723 Least number k such that n^k + (n+1)^k + ... + (n+k-1)^k is prime or 0 if no such number exists.

2, 1, 1, 2, 1, 0, 1, 0, 2, 0, 1, 2, 1, 2, 0, 6, 1, 0, 1, 0, 6, 2, 1, 2, 2, 0, 0, 0, 1, 2, 1, 2, 0, 2, 2, 0, 1, 0, 2, 0, 1, 2, 1, 0, 0, 0, 1, 6, 0, 2, 0, 0, 1, 0, 0, 0, 0, 6, 1, 2, 1, 0, 0, 0, 2, 0, 1, 0, 2, 2, 1, 2, 1, 0, 0, 6, 0, 0, 1, 0, 0, 2, 1, 2, 2, 0, 2, 0, 1, 2, 6

Offset: 1

Author

Derek Orr, May 30 2014

Keywords

• nonn

Comments

a(119) = 42. Is a(n) only equal to 0, 1, 2, 6, or 42?

a(n) = 0 is confirmed for k <= 500. See A242927.

Examples

			1^1 = 1 is not prime. 1^2+2^2 = 5 is prime. Thus a(1) = 2.
		

Links

• Derek Orr, Table of n, a(n) for n = 1..91

Crossrefs

Cf. A242927.

Programs

PARI

a(n)=for(k=1,500,if(ispseudoprime(sum(i=0,k-1,(n+i)^k)),return(k)))
n=1;while(n<200,print1(a(n),", ");n+=1)