The combinatorics of q-Hermite polynomials and the Askey-Wilson integral
European Journal of Combinatorics
Laguerre polynomials, weighted derangements, and positivity
SIAM Journal on Discrete Mathematics
A combinatorial formula for the linearization coefficients of general Sheffer polynomials
European Journal of Combinatorics
Combinatorics of generalized Tchebycheff polynomials
European Journal of Combinatorics
Generatingfunctionology
Euler--Mahonian statistics on ordered set partitions (II)
Journal of Combinatorial Theory Series A
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We propose a new approach to the combinatorial interpretations of linearization coefficient problem of orthogonal polynomials. We first establish a difference system and then solve it combinatorially and analytically using the method of separation of variables. We illustrate our approach by applying it to determine the number of perfect matchings, derangements, and other weighted permutation problems. The separation of variables technique naturally leads to integral representations of combinatorial numbers where the integrand contains a product of one or more types of orthogonal polynomials. This also establishes the positivity of such integrals.