A327240 - OEIS

%I #17 Sep 14 2019 12:26:47

%S 6,8,12,24,48,108,384,864,8748,995328,2348273369088,7421703487488,

%T 21422803359744,3470494144278528,161919374795459002368,

%U 1838129271989302091317248,2168345519443636233418208968704,28070062609828769223367060340342784

%N 3-smooth numbers k such that k-1 and (k-2)/2 are prime.

%C Numbers k of the form 2^a*3^b such that k-1 and (k-2)/2 are prime.

%C For all terms k except 6 and 8, k-2 is in A325204.

%C All terms except 6 and 12 end in 4 or 8.

%H Ray Chandler, <a href="/A327240/b327240.txt">Table of n, a(n) for n = 1..39</a> (terms < 10^1000)

%e a(3)=12 is a term because 12=2^2*3 and 11 and 10/2 are prime.

%t nmax = 10^35;

%t Select[Sort[Flatten[Table[2^i*3^j, {j, 0, Log[3, nmax]}, {i, Log[2, nmax/3^j]}]]], PrimeQ[# - 1] && PrimeQ[(# - 2)/2] &]

%Y Cf. A003586, A325204, A325255.

%K nonn

%O 1,1

%A _Ray Chandler_, Sep 14 2019