Direct bijective computation of the generating series for 2 and 3-connection coefficients of the symmetric group

Alejandro H. Morales¹ ; Ekaterina A. Vassilieva²

¹Université du Québec à Montréal
²Ecole Polytechnique, Palaiseau

The electronic journal of combinatorics, Tome 20 (2013) no. 2

Résumé

We evaluate combinatorially certain connection coefficients of the symmetric group that count the number of factorizations of a long cycle as a product of three permutations. Such factorizations admit an important topological interpretation in terms of unicellular constellations on orientable surfaces. Algebraic computation of these coefficients was first done by Jackson using irreducible characters of the symmetric group. However, bijective computations of these coefficients are so far limited to very special cases. Thanks to a new bijection that refines the work of Schaeffer and Vassilieva, we give an explicit closed form evaluation of the generating series for these coefficients. The main ingredient in the bijection is a modified oriented tricolored tree tractable to enumerate. Finally, reducing this bijection to factorizations of a long cycle into two permutations, we get the analogue formula for the corresponding generating series.

Détail

DOI : 10.37236/3226

Classification : 05A19, 05A15, 20B30
Mots-clés : connection coefficients, factorizations, cacti, symmetric group