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%I #12 Jan 05 2024 15:49:49
%S 1,10,21,25,31,1083,40485,82516
%N Numbers k such that (18^k + 1)^2 - 2 is prime.
%C Such primes are sometimes called Kynea primes of base 18.
%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((18^k+1)^2-2)&&print1(k,", "))
%Y Cf. A091513 (b=2), A100902 (b=6), A100904 (b=10), A364077 (b=12), A100906 (b=14), A364081 (b=20), A100908 (b=22).
%Y Cf. A364078.
%K nonn,hard,more
%O 1,2
%A _Jeppe Stig Nielsen_, Jul 03 2023