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A166718
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Numbers with at most 4 prime factors (counted with multiplicity)
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2
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1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76
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OFFSET
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1,2
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COMMENTS
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Maynard shows there are infinitely many integers n such that the interval [n,n+90] contains 2 primes and a number with at most 4 prime factors [Jonathan Vos Post, May 23 2012]
Subset of the 5-free numbers (numbers where each exponent in the prime factorization is <=4). - R. J. Mathar, Aug 08 2012
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LINKS
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FORMULA
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EXAMPLE
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88 = 2*2*2*11 is in the sequence since it has 4 prime factors
72 = 2*2*2*3*3 is not in the sequence since it has 5 prime factors
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MATHEMATICA
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Select[Range[100], PrimeOmega[#]<= 4 &] (* G. C. Greubel, May 24 2016 *)
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PROG
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(PARI) isA166718(n) = (bigomega(n) <= 4)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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