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Search: id:A036351
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| A036351 |
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Number of numbers <= 10^n which are products of two distinct primes. |
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+0
1
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| 2, 30, 288, 2600, 23313, 209867, 1903878, 17426029, 160785135, 1493766851, 13959963049, 131125938680, 1237087821006, 11715901643501
(list; graph; listen)
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OFFSET
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1,1
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LINKS
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Index entries for sequences related to numbers of primes in various ranges
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FORMULA
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(1/2)*( Pi(10^(n/2)) + Sum_{i=1..Pi(10^n)} Pi( (10^n-1)/P_i) ) -1 = Sum_{i=1..Pi(sqrt(10^n))} (Pi( (10^n-1)/P_i ) -1) - binomial( Pi(sqrt(10^n)), 2) (from Robert G. Wilson v (rgwv(AT)rgwv.com), May 19 2005)
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MATHEMATICA
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f[n_] := Sum[ PrimePi[(10^n - 1)/Prime[i]] - 1, {i, PrimePi[ Sqrt[10^n]]}] - Binomial[ PrimePi[ Sqrt[10^n]], 2]; Table[ f[n], {n, 10}] (from Robert G. Wilson v (rgwv(AT)rgwv.com), May 19 2005)
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CROSSREFS
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Cf. A066265.
Sequence in context: A007030 A157054 A092355 this_sequence A089433 A152277 A083446
Adjacent sequences: A036348 A036349 A036350 this_sequence A036352 A036353 A036354
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KEYWORD
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nonn
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AUTHOR
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Shyam Sunder Gupta (guptass(AT)rediffmail.com)
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EXTENSIONS
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a(14) from Robert G. Wilson v (rgwv(AT)rgwv.com), May 19 2005
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