A036352 Number of numbers up to 10^n that are products of two primes.

4, 34, 299, 2625, 23378, 210035, 1904324, 17427258, 160788536, 1493776443, 13959990342, 131126017178, 1237088048653, 11715902308080, 111329817298881, 1061057292827269, 10139482913717352, 97123037685177087, 932300026230174178, 8966605849641219022, 86389956293761485464

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: A155628 A346936 A356286 * A005569 A370171 A232910

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