mml=<math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mfenced separators="|"><mrow><mi>x</mi><mo>+</mo><mi>a</mi></mrow></mfenced><mi>n</mi></msup><mo>=</mo><munderover><mo>∑</mo><mi>k</mi><mo>=</mo></munderover><mfenced separators="|"><mfrac linethickness="0pt"><mi>n</mi><mi>k</mi></mfrac></mfenced><msup><mi>x</mi><mi>k</mi></msup><msup><mi>a</mi><mrow><mi>n</mi><mo>-</mo><mi>k</mi></mrow></msup></math>