%I #22 Jun 11 2021 08:48:58
%S 2,10,50,7900,18494,23840,36838
%N Numbers k such that absolute value of 9^k - k^9 is prime.
%C Three larger terms 18494, 23840 and 36838 found by _Donovan Johnson_, Jul-Aug 2005.
%t 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 *)
%o (PARI) is(n)=isprime(abs(9^n-n^9)) \\ _Charles R Greathouse IV_, Feb 17 2017
%Y Cf. A072180, A109387, A117705, A117706, A128447, A128448, A128450, A128451, A122003, A128453, A128454.
%K hard,more,nonn
%O 1,1
%A _Alexander Adamchuk_, Mar 03 2007
%E a(4)-a(6) from _Ryan Propper_, Feb 22 2008
%E a(7) from _Donovan Johnson_, Feb 26 2008
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