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Indices of primes in A049685.
1

%I #10 Dec 05 2023 16:43:23

%S 2,3,6,9,15,21,44,50,114

%N Indices of primes in A049685.

%C Related to the search of solutions of the pair of congruences p^2 == -5 (mod q), q^2 == -5 (mod p).

%C Cosgrave and Dilcher list terms up to 25000, including probable primes.

%H J. B. Cosgrave and K. Dilcher, <a href="https://fq.math.ca/Papers1/51-2/CosgraveDilcher-1.pdf">Pairs of reciprocal quadratic congruences involving primes</a>, Fib. Quart. 51 (2) (2013) 98, after Theorem 4.

%F A074281(n) = A049685(a(n)).

%F a(n) = (A074304(n)-1)/2.

%Y Cf. A049685, A074281, A074304.

%K nonn,more

%O 1,1

%A _R. J. Mathar_, Jul 22 2022