ピタゴラス平均
任意の i {\displaystyle i} と j {\displaystyle j} に対して
M  ( ... , x i , ... , x j , ... ) = M  ( ... , x j , ... , x i , ... ) {\displaystyle \operatorname {M} (\ldots ,\,x_{i},\,\ldots ,\,x_{j},\,\ldots )=\operatorname {M} (\ldots ,\,x_{j},\,\ldots ,\,x_{i},\,\ldots )}