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A257586
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Numbers that are neither primes nor three times primes.
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1
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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
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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a(n) ~ n*(1+(4/3)/log(n)).
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MAPLE
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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;
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MATHEMATICA
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Select[Range@96, Nor[PrimeQ[#], PrimeQ[#/3]]&] (* Ivan N. Ianakiev, May 08 2015 *)
Module[{nn=100, pr, pr3}, pr=Prime[Range[PrimePi[nn]]]; pr3=3Prime[Range[ PrimePi[ nn/3]]]; Complement[Range[nn], pr, pr3]] (* Harvey P. Dale, May 13 2020 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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