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Numbers k such that (9^k + 9*k)/9 is prime.
1

%I #8 Feb 29 2024 06:19:49

%S 1,2,4,8,10,28,1348,1424,12838

%N Numbers k such that (9^k + 9*k)/9 is prime.

%C If it exists, a(10) > 50000.

%o (PARI) is(n) = ispseudoprime(9^(n-1)+n)

%Y Cf. A221911, A226202.

%K nonn,hard,more

%O 1,2

%A _Hugo Pfoertner_, Feb 27 2024