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A070915 Numbers having at most two distinct prime factors. 2
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, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 61, 62, 63, 64, 65, 67, 68, 69, 71 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..10000

FORMULA

a(n) ~ n log n/log log n. - Charles R Greathouse IV, Oct 16 2015

EXAMPLE

88 and 77 are terms, as 88=11*2^3 and 77=11*7, but 66 is not a term, as 66 = 11*3*2.

MATHEMATICA

Select[Range[80], PrimeNu[#]<3&] (* Harvey P. Dale, Sep 19 2012 *)

PROG

(PARI) is(n)=omega(n)<3 \\ Charles R Greathouse IV, Oct 16 2015

CROSSREFS

A000040, A000961, A006681 and A003586 are subsequences.

Cf. A001221(a(n)) <= 2, A007774.

Sequence in context: A281873 A273888 A192218 * A004441 A004438 A109425

Adjacent sequences:  A070912 A070913 A070914 * A070916 A070917 A070918

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, May 20 2002

STATUS

approved

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Last modified April 21 22:12 EDT 2019. Contains 322328 sequences. (Running on oeis4.)