when I read an article,I find it seems there is a conclusion like the followings.

$H$ is an Hopf algebra(or an abstract group). Then $dimH=\sum_{V:simple ~module ~of ~H}(dimV)^2$.

who can tell me where I can find this content?Thank you very much.

oh...It seems $H$ need to be semisimple!

Oh...I think I already understand this.~When $H$ is a semisimple algebra.The above conclusion is right.For any Hopf algebra,maybe it's wrong. So please vote to close.Thanks everyone!