A141797 -id:A141797 - cp's OEIS frontend

A141798 Numbers n such that 2*23^n + 1 is prime.

0, 1, 5, 21, 261, 47589, 93337

Offset: 1

Rick L. Shepherd, Jul 05 2008

Primes found and proved by PrimeForm. No more terms up to 20000.
a(6) and a(7) proved prime by the primality proving program LLR. - Robert Price, Jan 06 2016
a(8) > 2*10^5. - Robert Price, Jan 06 2016

Cf. A141774, A141797, A141802, A190942, A068231.

Join[{0}, Select[Range[1, 261, 2], PrimeQ[2*23^# + 1] &]] (* Arkadiusz Wesolowski, Nov 06 2012 *)

is(n)=ispseudoprime(2*23^n+1) \\ Charles R Greathouse IV, Feb 20 2017

a(6)-a(7) from Robert Price, Jan 06 2016

A332763 Numbers k such that 6*17^k + 1 is prime.

Original entry on oeis.org

0, 1, 5, 7, 19, 23, 67, 107, 400, 429, 617, 743, 1065, 7717, 12329, 14459, 22425, 114543, 221983, 237453

Offset: 1

Paul S. Vanderveen, Feb 22 2020

a(21) > 3.75*10^5. - Paul S. Vanderveen, Jul 05 2020

Cf. A141797.

Select[Range[0, 1000], PrimeQ[6*17^# + 1] &] (* Amiram Eldar, Feb 24 2020 *)

for(i=1,10000, if( ispseudoprime(6*17^i+1), print1(i, ", ")));

a(19) from Paul S. Vanderveen, Mar 09 2020

a(20) from Paul S. Vanderveen, Mar 15 2020

cp's OEIS Frontend

A141798 Numbers n such that 2*23^n + 1 is prime.

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