Lah number

Lah numbers, discovered by Ivo Lah in 1955 are coefficients expressing rising factorials in terms of falling factorials. Unsigned Lah numbers have an interesting meaning in combinatorics: they count the number of ways a set of n elements can be partitioned into k nonempty subsets that are linearly ordered. Lah numbers are related to Stirling numbers.

Unsigned Lah numbers:

Signed Lah numbers