A364080 - OEIS

%I #12 Jan 05 2024 15:58:05

%S 1,2,53,183,1281,1300,8041,29936,72820

%N Numbers k such that (20^k - 1)^2 - 2 is prime.

%C Such primes are sometimes called Carol primes of base 20.

%H Prime-Wiki, <a href="https://www.rieselprime.de/ziki/Carol-Kynea_prime">Carol-Kynea prime</a>.

%H Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Near-SquarePrime.html">Near-Square Prime</a>.

%o (PARI) for(k=1,1200,ispseudoprime((20^k-1)^2-2)&&print1(k,", "))

%Y Cf. A091515 (b=2), A100901 (b=6), A100903 (b=10), A364076 (b=12), A100905 (b=14), A364078 (b=18), A100907 (b=22).

%Y Cf. A364081.

%K nonn,hard,more

%O 1,2

%A _Jeppe Stig Nielsen_, Jul 03 2023