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A036352 Number of numbers up to 10^n that are products of two primes. 15
4, 34, 299, 2625, 23378, 210035, 1904324, 17427258, 160788536, 1493776443, 13959990342, 131126017178, 1237088048653, 11715902308080, 111329817298881, 1061057292827269, 10139482913717352, 97123037685177087, 932300026230174178, 8966605849641219022, 86389956293761485464 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..21.

MATHEMATICA

SemiPrimePi[n_] := Sum[ PrimePi[n/Prime@ i] - i + 1, {i, PrimePi@ Sqrt@ n}]; Array[ SemiPrimePi[10^#] &, 14] (* Robert G. Wilson v, Feb 12 2015 *)

PROG

(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

CROSSREFS

Essentially the same as A066265.

Sequence in context: A216239 A201684 A155628 * A005569 A232910 A208215

Adjacent sequences:  A036349 A036350 A036351 * A036353 A036354 A036355

KEYWORD

nonn

AUTHOR

Shyam Sunder Gupta

EXTENSIONS

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

STATUS

approved

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Last modified February 20 22:51 EST 2019. Contains 320362 sequences. (Running on oeis4.)