<?xml version="1.0" encoding="UTF-8"?>
<math xmlns="http://www.w3.org/1998/Math/MathML">
   <mfenced close=")" open="(">
      <mrow>
         <mn>1</mn>
         <mo>+</mo>
         <mn>2</mn>
         <mo>+</mo>
         <mi>…</mi>
         <mo>+</mo>
         <mi>k</mi>
         <mo>+</mo>
         <mi>…</mi>
         <mo>+</mo>
         <mfenced close=")" open="(">
            <mrow>
               <mi>n</mi>
               <mo>-</mo>
               <mn>1</mn>
            </mrow>
         </mfenced>
      </mrow>
   </mfenced>
</math>
