Lah number

Mathematical sequence

In mathematics, the (signed and unsigned) Lah numbers are coefficients expressing rising factorials in terms of falling factorials and vice versa. They were discovered by Ivo Lah in 1954. Explicitly, the unsigned Lah numbers L ( n , k) {\displaystyle L(n,k)} are given by the formula involving the binomial coefficient L ( n , k) = ( n − 1 k − 1) n !

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