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 A327240 3-smooth numbers k such that k-1 and (k-2)/2 are prime. 3
 6, 8, 12, 24, 48, 108, 384, 864, 8748, 995328, 2348273369088, 7421703487488, 21422803359744, 3470494144278528, 161919374795459002368, 1838129271989302091317248, 2168345519443636233418208968704, 28070062609828769223367060340342784 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers k of the form 2^a*3^b such that k-1 and (k-2)/2 are prime. For all terms k except 6 and 8, k-2 is in A325204. All terms except 6 and 12 end in 4 or 8. LINKS Ray Chandler, Table of n, a(n) for n = 1..39 (terms < 10^1000) EXAMPLE a(3)=12 is a term because 12=2^2*3 and 11 and 10/2 are prime. MATHEMATICA nmax = 10^35; Select[Sort[Flatten[Table[2^i*3^j, {j, 0, Log[3, nmax]}, {i, Log[2, nmax/3^j]}]]], PrimeQ[# - 1] && PrimeQ[(# - 2)/2] &] CROSSREFS Cf. A003586, A325204, A325255. Sequence in context: A315873 A072057 A212351 * A274001 A324212 A160133 Adjacent sequences:  A327237 A327238 A327239 * A327241 A327242 A327243 KEYWORD nonn AUTHOR Ray Chandler, Sep 14 2019 STATUS approved

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Last modified June 22 21:29 EDT 2021. Contains 345393 sequences. (Running on oeis4.)