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A335799 a(n) is the least number k such that 3^k-2 and 3^k+2 are the product of n prime factors counted with multiplicity. 0
2, 12, 18, 38, 79, 75, 153, 313 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A001222(3^k-2) = A001222(3^k+2).

a(9) >= 521, a(10) >= 368, a(11) >= 339, a(12) >= 551. - Chai Wah Wu, Sep 23 2020

LINKS

Table of n, a(n) for n=1..8.

EXAMPLE

a(1) = 2 because 3^2-2 = 7 and 3^2+2 = 11 are both prime.

MATHEMATICA

m = 6; s = Table[0, {m}]; c = 0; k = 1; While[c < m, n = PrimeOmega[3^k - 2]; If[n <= m && s[[n]] == 0, n2 = PrimeOmega[3^k + 2]; If[n2 == n, s[[n]] = k; c++]]; k++]; s (* Amiram Eldar, Sep 18 2020 *)

PROG

(PARI) a(n) = {my(k=1); while((bigomega(3^k-2) != n) || (bigomega(3^k+2) != n), k++); k; } \\ Michel Marcus, Sep 14 2020

CROSSREFS

Cf. A000040, A001222, A001358, A014224.

Sequence in context: A281353 A257256 A325767 * A190044 A066238 A101074

Adjacent sequences:  A335796 A335797 A335798 * A335800 A335801 A335802

KEYWORD

nonn,more

AUTHOR

Zak Seidov, Sep 13 2020

EXTENSIONS

a(8) from Daniel Suteu, Sep 14 2020

STATUS

approved

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Last modified October 25 14:20 EDT 2021. Contains 348253 sequences. (Running on oeis4.)