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%I #25 Jul 20 2018 03:53:37
%S 2,3,6,12,15,21,27,42,45,57,66,87,90,96,117,120,126,141,147,180,210,
%T 216,222,246,255,297,321,327,330,342,360,372,381,405,456,477,507,510,
%U 516,525,552,612,615,645,705,720,726,741,750,756,780,792,801,867,906,945
%N Numbers n such that 2n-1 and 4n-1 are primes.
%H Muniru A Asiru, <a href="/A124485/b124485.txt">Table of n, a(n) for n = 1..5000</a>
%F a(n) = (A005384(n+1) + 1)/2. - _Hilko Koning_, Jul 19 2018
%p select(k->isprime(2*k-1) and isprime(4*k-1),[$1..1000]); # _Muniru A Asiru_, Jul 19 2018
%t Select[Range[1000], And @@ PrimeQ /@ ({2, 4}*# - 1) &] (* _Ray Chandler_, Nov 21 2006 *)
%o (GAP) Filtered([1..1000],p->IsPrime(2*p-1) and IsPrime(4*p-1)); # _Muniru A Asiru_, Jul 19 2018
%Y Cf. A005384 (Sophie Germain primes).
%Y Cf. A124486, A124487, A124488, A124489, A124490, A124491, A124492.
%K nonn
%O 1,1
%A _Artur Jasinski_, Nov 04 2006
%E Extended by _Ray Chandler_, Nov 21 2006
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