id:A111939 - OEIS Search Results

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A111939

Number of primes < semiprime(n).

+0
2

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; listen)

	OFFSET	`1,1`
	FORMULA	`a(n) = A000720(A001358(n)).`
	MATHEMATICA	`PrimePi@Select[Range@218, Plus @@ Last /@ FactorInteger@# == 2 &] (from Robert G. Wilson v (rgwv(at)rgwv.com), Jan 10 2006)`
	CROSSREFS	`Cf. A122489.` `Sequence in context: A063208 A092988 A138768 this_sequence A003962 A102443 A102441` `Adjacent sequences: A111936 A111937 A111938 this_sequence A111940 A111941 A111942`
	KEYWORD	`nonn`
	AUTHOR	`Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Nov 27 2005`
	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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Last modified November 24 23:16 EST 2009. Contains 167481 sequences.

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