centerbaseline=false mml=<math xmlns="http://www.w3.org/1998/Math/MathML"><munderover><mo>∑</mo><mrow><mi mathvariant="normal">n</mi><mo>=</mo><mn>1</mn></mrow><mi mathvariant="normal">∞</mi></munderover><msub><mi mathvariant="normal">U</mi><mi mathvariant="normal">n</mi></msub></math>