An mn element represents a "numeric literal" or other data that should be rendered as a numeric literal. Generally speaking, a numeric literal is a sequence of digits, perhaps including a decimal point, representing an unsigned integer or real number. MathML Fundamentals

<math> <mn>34</mn> <mo>+</mo> <mn mathvariant="bold">102.56</mn> <mo>+</mo> <mn mathcolor="#ff0000">666</mn> <mo>+</mo> <mn>34e-1</mn> </math>