Search: id:A036351
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%I A036351
%S A036351 2,30,288,2600,23313,209867,1903878,17426029,160785135,1493766851,
%T A036351 13959963049,131125938680,1237087821006,11715901643501
%N A036351 Number of numbers <= 10^n which are products of two distinct primes.
%H A036351 <a href="Sindx_Pri.html#primepop">Index entries for sequences related 
               to numbers of primes in various ranges</a>
%F A036351 (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)
%t A036351 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)
%Y A036351 Cf. A066265.
%Y A036351 Sequence in context: A007030 A157054 A092355 this_sequence A089433 A152277 
               A083446
%Y A036351 Adjacent sequences: A036348 A036349 A036350 this_sequence A036352 A036353 
               A036354
%K A036351 nonn
%O A036351 1,1
%A A036351 Shyam Sunder Gupta (guptass(AT)rediffmail.com)
%E A036351 a(14) from Robert G. Wilson v (rgwv(AT)rgwv.com), May 19 2005

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