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http://functions.wolfram.com/13.04.06.0004.01
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PrimePi[n] == Sum[(k - 2)! - k Floor[(k - 2)!/k], {k, 3, n}] - 1 /;
Element[n - 3, Integers] && n - 3 > 0
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Cell[BoxData[RowBox[List[RowBox[List[RowBox[List["PrimePi", "[", "n", "]"]], "\[Equal]", RowBox[List[RowBox[List[UnderoverscriptBox["\[Sum]", RowBox[List["k", "=", "3"]], "n"], RowBox[List["(", RowBox[List[RowBox[List[RowBox[List["(", RowBox[List["k", "-", "2"]], ")"]], "!"]], "-", RowBox[List["k", " ", RowBox[List["Floor", "[", FractionBox[RowBox[List[RowBox[List["(", RowBox[List["k", "-", "2"]], ")"]], "!"]], "k"], "]"]]]]]], ")"]]]], "-", "1"]]]], "/;", RowBox[List[RowBox[List[RowBox[List["n", "-", "3"]], "\[Element]", "Integers"]], "\[And]", RowBox[List[RowBox[List["n", "-", "3"]], ">", "0"]]]]]]]]
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<math xmlns='http://www.w3.org/1998/Math/MathML' mathematica:form='TraditionalForm' xmlns:mathematica='http://www.wolfram.com/XML/'> <semantics> <mrow> <mrow> <mrow> <semantics> <mi> π </mi> <annotation encoding='Mathematica'> TagBox["\[Pi]", PrimePi] </annotation> </semantics> <mo> ( </mo> <mi> n </mi> <mo> ) </mo> </mrow> <mo> ⩵ </mo> <mrow> <mrow> <munderover> <mo> ∑ </mo> <mrow> <mi> k </mi> <mo> = </mo> <mn> 3 </mn> </mrow> <mi> n </mi> </munderover> <mrow> <mo> ( </mo> <mrow> <mrow> <mrow> <mo> ( </mo> <mrow> <mi> k </mi> <mo> - </mo> <mn> 2 </mn> </mrow> <mo> ) </mo> </mrow> <mo> ! </mo> </mrow> <mo> - </mo> <mrow> <mi> k </mi> <mo> ⁢ </mo> <mrow> <mo> ⌊ </mo> <mfrac> <mrow> <mrow> <mo> ( </mo> <mrow> <mi> k </mi> <mo> - </mo> <mn> 2 </mn> </mrow> <mo> ) </mo> </mrow> <mo> ! </mo> </mrow> <mi> k </mi> </mfrac> <mo> ⌋ </mo> </mrow> </mrow> </mrow> <mo> ) </mo> </mrow> </mrow> <mo> - </mo> <mn> 1 </mn> </mrow> </mrow> <mo> /; </mo> <mrow> <mrow> <mi> n </mi> <mo> - </mo> <mn> 3 </mn> </mrow> <mo> ∈ </mo> <msup> <mi> ℕ </mi> <mo> + </mo> </msup> </mrow> </mrow> <annotation-xml encoding='MathML-Content'> <apply> <ci> Condition </ci> <apply> <eq /> <apply> <ci> PrimePi </ci> <ci> n </ci> </apply> <apply> <plus /> <apply> <sum /> <bvar> <ci> k </ci> </bvar> <lowlimit> <cn type='integer'> 3 </cn> </lowlimit> <uplimit> <ci> n </ci> </uplimit> <apply> <plus /> <apply> <factorial /> <apply> <plus /> <ci> k </ci> <cn type='integer'> -2 </cn> </apply> </apply> <apply> <times /> <cn type='integer'> -1 </cn> <apply> <times /> <ci> k </ci> <apply> <floor /> <apply> <times /> <apply> <factorial /> <apply> <plus /> <ci> k </ci> <cn type='integer'> -2 </cn> </apply> </apply> <apply> <power /> <ci> k </ci> <cn type='integer'> -1 </cn> </apply> </apply> </apply> </apply> </apply> </apply> </apply> <cn type='integer'> -1 </cn> </apply> </apply> <apply> <in /> <apply> <plus /> <ci> n </ci> <cn type='integer'> -3 </cn> </apply> <apply> <ci> SuperPlus </ci> <ci> ℕ </ci> </apply> </apply> </apply> </annotation-xml> </semantics> </math>
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| Cell[BoxData[RowBox[List[RowBox[List["HoldPattern", "[", RowBox[List["PrimePi", "[", "n_", "]"]], "]"]], "\[RuleDelayed]", RowBox[List[RowBox[List[RowBox[List[UnderoverscriptBox["\[Sum]", RowBox[List["k", "=", "3"]], "n"], RowBox[List["(", RowBox[List[RowBox[List[RowBox[List["(", RowBox[List["k", "-", "2"]], ")"]], "!"]], "-", RowBox[List["k", " ", RowBox[List["Floor", "[", FractionBox[RowBox[List[RowBox[List["(", RowBox[List["k", "-", "2"]], ")"]], "!"]], "k"], "]"]]]]]], ")"]]]], "-", "1"]], "/;", RowBox[List[RowBox[List[RowBox[List["n", "-", "3"]], "\[Element]", "Integers"]], "&&", RowBox[List[RowBox[List["n", "-", "3"]], ">", "0"]]]]]]]]]] |
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Date Added to functions.wolfram.com (modification date)
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