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

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

Offset

1,1

Comments

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

Links

Table of n, a(n) for n=1..7.

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 *)

Prog

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

Crossrefs

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

Sequence in context: A205772 A306336 A074140 * A037514 A037717 A019476

Adjacent sequences: A128446 A128447 A128448 * A128450 A128451 A128452

Keyword

hard,more,nonn

Author

Alexander Adamchuk, Mar 03 2007

Extensions

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

a(7) from Donovan Johnson, Feb 26 2008

Status

approved