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

2, 6, 20, 24, 18582, 20366

Offset

1,1

Comments

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

Links

Table of n, a(n) for n=1..6.

Henri Lifchitz and Renaud Lifchitz, PRP Records.

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 *)

Prog

(PARI) is(n)=isprime(abs(7^n-n^7)) \\ Charles R Greathouse IV, Feb 17 2017

Crossrefs

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

Sequence in context: A370974 A370968 A343506 * A032622 A104749 A062281

Adjacent sequences: A128444 A128445 A128446 * A128448 A128449 A128450

Keyword

nonn,hard,more

Author

Alexander Adamchuk, Mar 03 2007

Extensions

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

Status

approved