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Numbers k for which 2*k-1, 4*k-1 and 8*k-1 are primes.
7

%I #8 Mar 27 2020 09:02:40

%S 3,6,21,45,90,180,255,360,510,516,615,705,726,741,756,906,945,951,966,

%T 1230,1350,1410,1725,1746,1770,1911,1956,2541,2700,2721,2925,3051,

%U 3066,3225,3540,3576,3675,3951,4485,4611,5295,5346,5355,5586,5736,5775,5901

%N Numbers k for which 2*k-1, 4*k-1 and 8*k-1 are primes.

%H Amiram Eldar, <a href="/A124493/b124493.txt">Table of n, a(n) for n = 1..10000</a>

%t Select[3*Range[2000], And @@ PrimeQ /@ ({2, 4, 8}*# - 1) &] (* _Ray Chandler_, Nov 22 2006 *)

%Y Cf. A006254, A124485, A124494, A124017, A125113, A124514, A124515, A124516.

%K nonn

%O 1,1

%A _Artur Jasinski_, Nov 04 2006