This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A242922 Least number k such that (k^n+n^k)/(k+n) is prime or 0 if no such k exists. 1
 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, 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, 0, 0, 1795, 0, 0, 0, 0, 0, 0, 0, 0, 0, 53, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS If a(i) = j, then a(j) = i for any i and j. 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. LINKS EXAMPLE (8^3+3^8)/(8+3) = 7073/11 = 643 is prime. Thus, a(3) = 8 and a(8) = 3. PROG (PARI) a(n)=for(k=1, 5000, s=(k^n+n^k)/(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: A246516 A095217 A230915 * A242530 A073410 A021361 Adjacent sequences:  A242919 A242920 A242921 * A242923 A242924 A242925 KEYWORD nonn,hard,more AUTHOR Derek Orr, May 26 2014 EXTENSIONS 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 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified October 18 15:21 EDT 2019. Contains 328162 sequences. (Running on oeis4.)