多重指数
( α β ) = α ! β ! ( α − β ) ! := ( α 1 β 1 ) ( α 2 β 2 ) ⋯ ( α n β n ) {\displaystyle {\binom {\alpha }{\beta }}={\frac {\alpha !}{\beta !(\alpha -\beta )!}}:={\binom {\alpha _{1}}{\beta _{1}}}{\binom {\alpha _{2}}{\beta _{2}}}\cdots {\binom {\alpha _{n}}{\beta _{n}}}}