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. Namely, 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.
- We need a definition here.