Cores with distinct parts and bigraded Fibonacci numbers

2017/05/28 by Paramonov, Kirill
#Combinatorics (math.CO) #FOS: Mathematics

paper · doi:10.48550/arxiv.1705.09991

Abstract

The notion of (a,b)-cores is closely related to rational (a,b) Dyck paths due to Anderson's bijection, and thus the number of (a,a+1)-cores is given by the Catalan number C_a. Recent research shows that (a,a+1) cores with distinct parts are enumerated by another important sequence- Fibonacci numbers F_a. In this paper, we consider the abacus description of (a,b)-cores to introduce the natural grading and generalize this result to (a,as+1)-cores. We also use the bijection with Dyck paths to count the number of (2k-1,2k+1)-cores with distinct parts. We give a second grading to Fibonacci numbers, induced by bigraded Catalan sequence C_a,b (q,t).

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