A128447 Numbers k such that absolute value of 7^k - k^7 is prime.

2, 6, 20, 24, 18582, 20366

Offset: 1

Author

Alexander Adamchuk, Mar 03 2007

Keywords

• nonn
• hard
• more

Comments

From the Lifchitz link: 116240, 188858, and 230492 are also terms. - Michael S. Branicky, Jul 29 2024

Links

• Henri Lifchitz and Renaud Lifchitz, PRP Records.

Crossrefs

Cf. A072180, A109387, A117705, A117706, A128448, A128449, A128450, A128451, A122003, A128453, A128454.

Programs

Mathematica

lst={};k=7;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(7^n-n^7)) \\ Charles R Greathouse IV, Feb 17 2017

Extensions

a(5) and a(6) from Donovan Johnson, Mar 03 2008