%I #13 Sep 08 2022 08:46:08

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

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

%H Steven Harvey, <a href="http://harvey563.tripod.com/GeneralizedWoodallPrimes.txt">Generalized Woodall Search</a>

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

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

%o (PARI) is(n)=ispseudoprime(n*7^n-1) \\ _Charles R Greathouse IV_, May 22 2017

%Y 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).

%K nonn,more

%O 1,1

%A _Vincenzo Librandi_, May 09 2014

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