

A242803


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


0



3, 4, 3, 0, 4, 491, 9, 5, 3, 4, 0, 16, 0, 7, 5, 0, 4, 20, 5, 85, 3, 64, 25, 15, 625, 0, 10, 0, 7, 19, 7, 9, 0, 15, 5, 0, 0, 4, 16, 25, 0, 0, 17, 11, 0, 16, 5, 0, 0, 7, 31, 0, 31, 100, 5, 0, 0, 0, 4, 0, 0, 0, 9, 0, 13, 0, 0, 0, 7, 0, 10, 0, 5, 0, 0, 0, 0, 0, 51, 0, 0, 0, 0, 136
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OFFSET

1,1


COMMENTS

a(n) = 0 is confirmed only for k <= 5000, they are not definite.


LINKS

Table of n, a(n) for n=1..84.


EXAMPLE

(1^1+3)/(1+3) = 1 is not prime. (2^2+3)/(2+3) = 7/5 is not prime. (3^3+3)/(3+3) = 30/6 = 5 is prime. Thus a(3)= 3.


PROG

(PARI) a(n)=for(k=1, 1500, s=(k^k+n)/(k+n); if(floor(s)==s, if(ispseudoprime(s), return(k))));
n=1; while(n<100, print(a(n)); n+=1)


CROSSREFS

Sequence in context: A244042 A318840 A318830 * A064460 A108481 A078070
Adjacent sequences: A242800 A242801 A242802 * A242804 A242805 A242806


KEYWORD

nonn,more,hard


AUTHOR

Derek Orr, May 23 2014


STATUS

approved



