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Numbers k such that (7^k + 7*k)/7 is prime.
2

%I #5 Feb 28 2024 13:24:41

%S 1,4,36,160,342,1086,2094,11524

%N Numbers k such that (7^k + 7*k)/7 is prime.

%C If it exists, a(11) > 50000.

%o (PARI) is(n) = ispseudoprime(7^(n-1)+n)

%Y Cf. A221909, A226199, A370657.

%Y Cf. A370190, A370661.

%K nonn,hard,more

%O 1,2

%A _Hugo Pfoertner_, Feb 24 2024