A128449 Numbers k such that absolute value of 9^k - k^9 is prime.

2, 10, 50, 7900, 18494, 23840, 36838

Offset: 1

Author

Alexander Adamchuk, Mar 03 2007

Keywords

• hard
• more
• nonn

Comments

Three larger terms 18494, 23840 and 36838 found by Donovan Johnson, Jul-Aug 2005.

From the Lifchitz link: 83024 is also a term. - Michael S. Branicky, Jul 29 2024

Links

• Henri Lifchitz and Renaud Lifchitz, PRP Records.

Crossrefs

Cf. A072180, A109387, A117705, A117706, A128447, A128448, A128450, A128451, A122003, A128453, A128454.

Programs

Mathematica

lst={};k=9;Do[If[PrimeQ[Abs[k^n-n^k]], AppendTo[lst, n]], {n, 0, 10^4}];lst (* Vladimir Joseph Stephan Orlovsky, Sep 10 2008 *)

PARI

is(n)=isprime(abs(9^n-n^9)) \\ Charles R Greathouse IV, Feb 17 2017

Extensions

a(4)-a(6) from Ryan Propper, Feb 22 2008

a(7) from Donovan Johnson, Feb 26 2008