<<< omml
<?xml version="1.0" encoding="UTF-8"?>
<m:oMathPara>
  <m:oMathParaPr>
    <m:jc m:val="center" />
  </m:oMathParaPr>
  <m:oMath>
    <m:r>
      <m:rPr>
        <m:sty m:val="b" />
      </m:rPr>
      <m:t>C</m:t>
    </m:r>
    <m:r>
      <m:rPr>
        <m:sty m:val="p" />
      </m:rPr>
      <m:t>(</m:t>
    </m:r>
    <m:r>
      <m:rPr>
        <m:sty m:val="p" />
      </m:rPr>
      <m:t>n</m:t>
    </m:r>
    <m:r>
      <m:rPr>
        <m:sty m:val="p" />
      </m:rPr>
      <m:t>,</m:t>
    </m:r>
    <m:r>
      <m:rPr>
        <m:sty m:val="p" />
      </m:rPr>
      <m:t>k</m:t>
    </m:r>
    <m:r>
      <m:rPr>
        <m:sty m:val="p" />
      </m:rPr>
      <m:t>)</m:t>
    </m:r>
    <m:r>
      <m:rPr>
        <m:sty m:val="p" />
      </m:rPr>
      <m:t>=</m:t>
    </m:r>
    <m:sSubSup>
      <m:e>
        <m:r>
          <m:rPr>
            <m:sty m:val="b" />
          </m:rPr>
          <m:t>C</m:t>
        </m:r>
      </m:e>
      <m:sub>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>k</m:t>
        </m:r>
      </m:sub>
      <m:sup>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>n</m:t>
        </m:r>
      </m:sup>
    </m:sSubSup>
    <m:r>
      <m:rPr>
        <m:sty m:val="p" />
      </m:rPr>
      <m:t>=</m:t>
    </m:r>
    <m:sSub>
      <m:e />
      <m:sub>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>n</m:t>
        </m:r>
      </m:sub>
    </m:sSub>
    <m:sSub>
      <m:e>
        <m:r>
          <m:rPr>
            <m:sty m:val="b" />
          </m:rPr>
          <m:t>C</m:t>
        </m:r>
      </m:e>
      <m:sub>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>k</m:t>
        </m:r>
      </m:sub>
    </m:sSub>
    <m:r>
      <m:rPr>
        <m:sty m:val="p" />
      </m:rPr>
      <m:t>=</m:t>
    </m:r>
    <m:d>
      <m:dPr>
        <m:begChr m:val="(" />
        <m:endChr m:val=")" />
        <m:grow />
      </m:dPr>
      <m:e>
        <m:f>
          <m:fPr>
            <m:type m:val="noBar" />
          </m:fPr>
          <m:num>
            <m:r>
              <m:rPr>
                <m:sty m:val="p" />
              </m:rPr>
              <m:t>n</m:t>
            </m:r>
          </m:num>
          <m:den>
            <m:r>
              <m:rPr>
                <m:sty m:val="p" />
              </m:rPr>
              <m:t>k</m:t>
            </m:r>
          </m:den>
        </m:f>
      </m:e>
    </m:d>
    <m:r>
      <m:rPr>
        <m:sty m:val="p" />
      </m:rPr>
      <m:t>=</m:t>
    </m:r>
    <m:f>
      <m:fPr>
        <m:type m:val="bar" />
      </m:fPr>
      <m:num>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>n</m:t>
        </m:r>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>!</m:t>
        </m:r>
      </m:num>
      <m:den>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>k</m:t>
        </m:r>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>!</m:t>
        </m:r>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t> </m:t>
        </m:r>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>(</m:t>
        </m:r>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>n</m:t>
        </m:r>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>−</m:t>
        </m:r>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>k</m:t>
        </m:r>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>)</m:t>
        </m:r>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>!</m:t>
        </m:r>
      </m:den>
    </m:f>
  </m:oMath>
</m:oMathPara>

>>> native
[ EStyled TextBold [ EIdentifier "C" ]
, ESymbol Open "("
, EIdentifier "n"
, ESymbol Pun ","
, EIdentifier "k"
, ESymbol Close ")"
, ESymbol Rel "="
, ESubsup
    (EStyled TextBold [ EIdentifier "C" ])
    (EIdentifier "k")
    (EIdentifier "n")
, ESymbol Rel "="
, ESub (EGrouped []) (EIdentifier "n")
, ESub (EStyled TextBold [ EIdentifier "C" ]) (EIdentifier "k")
, ESymbol Rel "="
, EDelimited
    "("
    ")"
    [ Right (EFraction NoLineFrac (EIdentifier "n") (EIdentifier "k"))
    ]
, ESymbol Rel "="
, EFraction
    NormalFrac
    (EGrouped [ EIdentifier "n" , ESymbol Pun "!" ])
    (EGrouped
       [ EIdentifier "k"
       , ESymbol Pun "!"
       , ESpace (1 % 6)
       , ESymbol Open "("
       , EIdentifier "n"
       , ESymbol Bin "\8722"
       , EIdentifier "k"
       , ESymbol Close ")"
       , ESymbol Pun "!"
       ])
]