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A036352
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Number of numbers up to 10^n that are products of two primes.
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15
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4, 34, 299, 2625, 23378, 210035, 1904324, 17427258, 160788536, 1493776443, 13959990342, 131126017178, 1237088048653, 11715902308080, 111329817298881, 1061057292827269, 10139482913717352, 97123037685177087, 932300026230174178, 8966605849641219022, 86389956293761485464
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OFFSET
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1,1
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LINKS
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Table of n, a(n) for n=1..21.
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MATHEMATICA
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SemiPrimePi[n_] := Sum[ PrimePi[n/Prime@ i] - i + 1, {i, PrimePi@ Sqrt@ n}]; Array[ SemiPrimePi[10^#] &, 14] (* Robert G. Wilson v, Feb 12 2015 *)
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PROG
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(PARI) a(n)=my(s); forprime(p=2, sqrt(10^n), s+=primepi(10^n\p)); s-binomial(primepi(sqrt(10^n)), 2) \\ Charles R Greathouse IV, Apr 23 2012
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CROSSREFS
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Essentially the same as A066265.
Sequence in context: A155628 A346936 A356286 * A005569 A232910 A208215
Adjacent sequences: A036349 A036350 A036351 * A036353 A036354 A036355
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KEYWORD
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nonn
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AUTHOR
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Shyam Sunder Gupta
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EXTENSIONS
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a(14) from Robert G. Wilson v, May 16 2005
a(15)-a(16) from Donovan Johnson, Mar 18 2010
a(17)-a(18) from A066265, added by Jens Kruse Andersen, Aug 16 2014
a(19)-a(21) from Henri Lifchitz, Jul 04 2015
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STATUS
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approved
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