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A194895
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Difference between the number of semiprimes less than 10^n and the number of primes less than 10^n
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0
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0, -1, 9, 131, 1396, 13786, 131537, 1239745, 11665803, 109941002, 1038723932, 9841935529, 93518105160, 891022511814, 8510960557278, 81485246876212, 781818951793344
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OFFSET
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0,3
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COMMENTS
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LINKS
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EXAMPLE
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There are 2625 semiprimes less than 10^4 and there are 1229 primes less than 10^4, so a(4) = 2625 - 1229 = 1396.
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MATHEMATICA
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SemiPrimePi[n_] := Sum[ PrimePi[n/Prime@ i] - i + 1, {i, PrimePi@ Sqrt@ n}]; f[n_] := SemiPrimePi[10^n - 1] - PrimePi[10^n - 1]; Array[f, 15, 0] (* Robert G. Wilson v, Jul 05 2012 *)
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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