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

1,1

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.

Links

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

Example

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

Prog

(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)

Crossrefs

Cf. A242927.

Sequence in context: A259029 A286128 A197547 * A229541 A015488 A014570

Adjacent sequences: A239720 A239721 A239722 * A239724 A239725 A239726

Keyword

nonn

Author

Derek Orr, May 30 2014

Status

approved