2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/60057We study generating functions for the number of permutations on n letters avoiding 132 and an arbitrary permutation $τ$ on k letters, or containing $τ$ exactly once. In several interesting cases the generating function depends only on k and is expressed via Chebyshev polynomials of the second kind.10 pagesCombinatorics05A05; 05A15; 30B70; 42C05text