%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