A220703 Numbers k such that k^7 + 7*k + 7^k is prime.

2, 3, 17, 74, 120, 212, 528, 2348, 13820, 41268

Offset: 1

Author

Vincenzo Librandi, Jan 07 2013

Keywords

• nonn
• more

Crossrefs

Cf. A220528.

Programs

Mathematica

Select[Range[5000], PrimeQ[#^7 + 7*# + 7^#]&]

PARI

is(n)=ispseudoprime(n^7+7*n+7^n) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(9) from Michael S. Branicky, Jul 13 2023

a(10) from Michael S. Branicky, Oct 27 2024