The Jacobi-Stirling numbers of the second kind are the polynomial
sequence defined by
for ,
with
and
for positive integers
and
. The companion Jacobi-Stirling numbers of the first kind
satisfy
with the same boundary conditions. At ,
the two families specialize to the Legendre-Stirling
numbers of the second and first kinds, respectively; this simply sets
in the two recurrences.
The name "Jacobi" refers to the classical second-order Jacobi differential
operator, whose polynomial eigenfunctions are the Jacobi
polynomials. The Jacobi-Stirling numbers arise as connection coefficients for
polynomial bases associated with powers of this operator.