login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

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