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A156658 Primes p such that also 2*p+1 or (p-1)/2 is prime.

%I A156658 #21 Jul 22 2020 11:39:23
%S A156658 2,3,5,7,11,23,29,41,47,53,59,83,89,107,113,131,167,173,179,191,227,
%T A156658 233,239,251,263,281,293,347,359,383,419,431,443,467,479,491,503,509,
%U A156658 563,587,593,641,653,659,683,719,743,761,809,839,863,887,911,953,983,1013
%N A156658 Primes p such that also 2*p+1 or (p-1)/2 is prime.
%C A156658 Union of A005384 and A005385;
%C A156658 The intersection of A005384 and A005385 is given by A059455.
%C A156658 A156660(a(n)) + A156659(a(n)) > 0;
%C A156658 primes occurring in Cunningham chains of the first kind.
%C A156658 A156876 gives the number of these numbers <= n. [_Reinhard Zumkeller_, Feb 18 2009]
%H A156658 Robert Price, <a href="/A156658/b156658.txt">Table of n, a(n) for n = 1..14198</a>
%H A156658 Wikipedia, <a href="http://en.wikipedia.org/wiki/Sophie_Germain_prime">Sophie Germain prime</a>
%H A156658 Wikipedia, <a href="http://en.wikipedia.org/wiki/Safe_prime">Safe prime</a>
%H A156658 Wikipedia, <a href="http://en.wikipedia.org/wiki/Cunningham_chain">Cunningham chain</a>
%p A156658 select(t -> isprime(t) and (isprime(2*t+1) or isprime((t-1)/2)), [2,seq(p,p=3..10000,2)]); # _Robert Israel_, May 03 2016
%t A156658 Select[Prime@ Range@ 180, PrimeQ[2 # + 1] || PrimeQ[(# - 1)/2] &] (* _Michael De Vlieger_, Apr 06 2016 *)
%o A156658 (PARI) lista(nn) = {forprime(p=2, nn, if (isprime(2*p+1) || isprime((p-1)/2), print1(p, ", ")););} \\ _Michel Marcus_, Apr 06 2016
%Y A156658 Cf. A005384, A005385, A059500, A156659, A156660, A156876.
%K A156658 nonn
%O A156658 1,1
%A A156658 _Reinhard Zumkeller_, Feb 13 2009