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A111939
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Number of primes < semiprime(n).
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1
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2, 3, 4, 4, 6, 6, 8, 8, 9, 9, 11, 11, 11, 12, 12, 14, 15, 15, 16, 16, 16, 18, 18, 19, 21, 21, 22, 23, 23, 23, 24, 24, 24, 24, 27, 29, 30, 30, 30, 30, 30, 30, 31, 32, 32, 34, 34, 34, 34, 34, 36, 37, 37, 37, 38, 39, 40, 40, 42, 42, 42, 44, 46, 46, 46, 46, 46, 46, 47, 47, 47, 47, 47
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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FORMULA
| a(n) = A000720(A001358(n)).
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MATHEMATICA
| PrimePi@Select[Range@218, Plus @@ Last /@ FactorInteger@# == 2 &] (from Robert G. Wilson v (rgwv(at)rgwv.com), Jan 10 2006)
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CROSSREFS
| Cf. A122489.
Sequence in context: A063208 A092988 A138768 * A003962 A102443 A102441
Adjacent sequences: A111936 A111937 A111938 * A111940 A111941 A111942
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KEYWORD
| nonn
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AUTHOR
| Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Nov 27 2005
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(at)rgwv.com), Lambert Herrgesell (zero815(AT)googlemail.com) and Matthew Conroy (http://www.madandmoonly.com/doctormatt), Dec 16 2005
Entry revised by Ray Chandler (rayjchandler(AT)sbcglobal.net), Sep 20 2006
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