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A133498
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a(n) = floor(sqrt(pi(2^n))).
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1
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0, 1, 1, 2, 2, 3, 4, 5, 7, 9, 13, 17, 23, 32, 43, 59, 80, 110, 151, 208, 286, 394, 544, 751, 1038, 1436, 1989, 2757, 3825, 5309, 7375, 10251, 14257, 19839, 27621, 38473, 53613, 74742, 104241, 145436, 202985, 283401, 395804, 552957, 772733, 1080160, 1510297
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OFFSET
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0,4
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LINKS
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FORMULA
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EXAMPLE
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a(4)=2 because pi(2^4)=6 and the greatest integer less than or equal to sqrt(6) is 2.
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MATHEMATICA
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Table[ Floor[Sqrt[PrimePi[2^n]]], {n, 0, 25}] (* G. C. Greubel, Jan 13 2017 *)
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PROG
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(PARI) a(n) = sqrtint(primepi(2^n)); \\ Michel Marcus, Sep 05 2013
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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