喺代數拓撲入面，歐拉特徵數（）係一個拓撲唔變量（其實係更強嘅同倫唔變量），佢對好多種嘅拓撲空間都有定義，包括可微流形、CW-複形等等，通常都會用嚟表示佢。
In algebraic topology, Euler's eigennumber ( ) is a topological invariant (in fact, a stronger homotopy invariant), and he has defined many kinds of topological spaces, including micromanifolds, CW-complexes, etc., which are usually used to represent him.