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A325255 3-smooth numbers k such that k+1 and (k+2)/2 are prime. 3
2, 4, 12, 36, 72, 192, 1152, 2592, 2916, 1492992, 1990656, 5308416, 28311552, 6879707136, 1761205026816, 5566277615616, 79164837199872, 3799912185593856, 115422332637413376, 1332669751402954752, 4803028329503971872 (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.

All terms except 2 and 4 are in A325204.

All terms except 4 end in 2 or 6.

LINKS

Ray Chandler, Table of n, a(n) for n = 1..41 (terms < 10^1000, first 39 terms from Robert Israel)

EXAMPLE

a(3)=12 is a term because 12=2^2*3 and 13 and 14/2 are prime.

MAPLE

N:= 10^100: # to get terms <= N

sort(select(t -> isprime(t+1) and isprime((t+2)/2), [seq(seq(2^i*3^j, i = 1 .. ilog2(N/3^j)), j=0..floor(log[3](N)))]));

CROSSREFS

Cf. A003586, A325204, A327240.

Sequence in context: A112083 A089965 A202727 * A084716 A241208 A149837

Adjacent sequences:  A325252 A325253 A325254 * A325256 A325257 A325258

KEYWORD

nonn

AUTHOR

Robert Israel, Sep 05 2019

STATUS

approved

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Last modified October 16 07:07 EDT 2021. Contains 348041 sequences. (Running on oeis4.)