A242200 Numbers n such that n*7^n - 1 is prime.

2, 18, 68, 84, 3812, 14838, 51582

Offset: 1

Author

Vincenzo Librandi, May 09 2014

Keywords

• nonn
• more

Links

• Steven Harvey, Generalized Woodall Search

Crossrefs

Cf. numbers n such that n*k^n - 1 is prime. A002234 (k=2), A006553 (k=3), A086661 (k=4), A059676 (k=5), A059675 (k=6), this sequence (k=7), A242201 (k=8), A242202 (k=9), A059671 (k=10).

Programs

Magma

[n: n in [0..3000] | IsPrime(n*7^n-1)];

Mathematica

Select[Range[2000], PrimeQ[# 7^# - 1] &]

PARI

is(n)=ispseudoprime(n*7^n-1) \\ Charles R Greathouse IV, May 22 2017

Extensions

a(5) - a(7) from Harvey's list (see Links).