The index of a vector field with finitely many zeros on a compact, oriented manifold is the same as the Euler characteristic of the manifold.
Poincaré-Hopf Index Theorem
See also
Gauss-Bonnet FormulaExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Poincaré-Hopf Index Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Poincare-HopfIndexTheorem.html