%I #20 Oct 28 2021 16:07:36
%S 0,1,3,5,3,11,15,5,3,5,9,23,81,83,135,143,9,23,117,5,9,161,159,317,
%T 339,203,219,95,693,35,105,5,321,425,69,23,201,191,219,983,1101,371,
%U 747,287,429,743,2649,1355,81,233,237,635,2403,395,1125,1997,69,9005
%N a(n) is the least nonnegative integer k such that 2^n - k is a Sophie Germain prime.
%H Artsiom Palkounikau, <a href="/A345014/b345014.txt">Table of n, a(n) for n = 1..3072</a>
%F a(n) = (A057821(n+1) + 1)/2.
%t Table[k=0;While[!(PrimeQ[p=2^n-k]&&PrimeQ[2p+1]),k++];k,{n,58}] (* _Giorgos Kalogeropoulos_, Sep 15 2021 *)
%o (Python)
%o from sympy import isprime
%o def a(n):
%o k = 0
%o while True:
%o if isprime(2 ** n - k) and isprime(2 * (2 ** n - k) + 1):
%o return k
%o k += 1
%o print([a(i) for i in range(1, 21)])
%o (PARI) a(n) = my(k=0,p); while (!(isprime(p=2^n-k) && isprime(2*p+1)), k++); k; \\ _Michel Marcus_, Sep 15 2021
%Y Cf. A005384, A057821, A013603, A243916.
%K nonn
%O 1,3
%A _Artsiom Palkounikau_, Sep 15 2021
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