If OneNote is anything like Word you can use LaTeX notation once you are inside an equation environment (Alt + =). For example in Word typing Alt + = \int^1_2

If OneNote is anything like Word you can use LaTeX notation once you are inside an equation environment (Alt + =). For example in Word typing Alt + = \int^1_2 \sum^x_(x+1) \ge \sqrt(25) Would produce exactly what you would get in LaTeX. You can even copy/paste between applications that support MathML.