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A257586 Numbers that are neither primes nor three times primes. 1
1, 4, 8, 10, 12, 14, 16, 18, 20, 22, 24, 25, 26, 27, 28, 30, 32, 34, 35, 36, 38, 40, 42, 44, 45, 46, 48, 49, 50, 52, 54, 55, 56, 58, 60, 62, 63, 64, 65, 66, 68, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 88, 90, 91, 92, 94, 95, 96 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Arises in studying A254077.

LINKS

N. J. A. Sloane, Table of n, a(n) for n = 1..10000

FORMULA

a(n) ~ n*(1+(4/3)/log(n)).

MAPLE

s1:=[]: for n from 1 to 1000 do

  if isprime(n) or ( (n mod 3) = 0 and isprime(n/3)) then ; else s1:=[op(s1), n]; fi; od: s1;

MATHEMATICA

Select[Range@96, Nor[PrimeQ[#], PrimeQ[#/3]]&] (* Ivan N. Ianakiev, May 08 2015 *)

CROSSREFS

Cf. A254077.

Sequence in context: A155878 A029886 A102218 * A172458 A175226 A057166

Adjacent sequences:  A257583 A257584 A257585 * A257587 A257588 A257589

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, May 07 2015

STATUS

approved

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Last modified November 13 19:25 EST 2018. Contains 317149 sequences. (Running on oeis4.)