# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a242922 Showing 1-1 of 1 %I A242922 #15 Oct 21 2014 12:38:30 %S A242922 0,2,8,0,0,0,43,3,0,0,0,0,21,0,0,0,0,0,0,0,13,0,47,0,287,0,0,0,0,0,0, %T A242922 0,0,0,0,0,0,0,0,0,0,0,7,0,0,0,23,0,0,0,0,0,77,0,0,0,0,0,0,0,0,0,0,0, %U A242922 0,0,1795,0,0,0,0,0,0,0,0,0,53,0,0,0,0,0,0,0,0,0,0,0 %N A242922 Least number k such that (k^n+n^k)/(k+n) is prime or 0 if no such k exists. %C A242922 If a(i) = j, then a(j) = i for any i and j. %C A242922 a(n) = 0 is definite for n=1. For other n-values where a(n) = 0, it is confirmed for k <= 5000. These are only conjectural. %e A242922 (8^3+3^8)/(8+3) = 7073/11 = 643 is prime. Thus, a(3) = 8 and a(8) = 3. %o A242922 (PARI) a(n)=for(k=1,5000,s=(k^n+n^k)/(k+n);if(floor(s)==s,if(ispseudoprime(s),return(k)))) %o A242922 n=1;while(n<100,print(a(n));n+=1) %K A242922 nonn,hard,more %O A242922 1,2 %A A242922 _Derek Orr_, May 26 2014 %E A242922 We don't normally allow conjectural terms, except in special circumstances. This is one of those exceptions, for if we included only terms that are known for certain, not much of this sequence would remain. - _N. J. A. Sloane_, May 31 2014 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE