English

A Fibonacci analogue of Stirling numbers

Combinatorics 2016-07-01 v3

Abstract

Consider the Fibonacci numbers defined by setting F1=1=F2F_1=1=F_2 and Fn=Fn1+Fn2F_n =F_{n-1}+F_{n-2} for n3n \geq 3. We let nF!=F1Fnn_F! = F_1 \cdots F_n and (nk)F=nF!kF!(nk)F!\binom{n}{k}_F = \frac{n_F!}{k_F!(n-k)_F!}. Let (x)0=(x)0=1(x)_{\downarrow_0} = (x)_{\uparrow_0} = 1 and for k1k \geq 1, (x)k=x(x1)(xk+1)(x)_{\downarrow_k} = x(x-1) \cdots (x-k+1) and (x)k=x(x+1)(x+k1)(x)_{\uparrow_k} = x(x+1) \cdots (x+k-1). Then the Stirling numbers of the first and second kind are the connections coefficients between the usual power basis {xn:n0}\{x^n:n \geq 0\} and the falling factorial basis {(x)n:n0}\{(x)_{\downarrow_n}:n \geq 0\} in the polynomial ring Q[x]\mathbb{Q}[x] and the Lah numbers are the connections coefficients between the rising factorial basis {(x)n:n0}\{(x)_{\uparrow_n}:n \geq 0\} and the falling factorial basis {(x)n:n0}\{(x)_{\downarrow_n}:n \geq 0\} in the polynomial ring Q[x]\mathbb{Q}[x]. The goal of this paper is to find Fibonacci analogues for the Stirling numbers of the first and second kind and the Lah numbers. Our idea is to replace the falling factorial basis and the rising factorial basis by the Fibo-falling factorial basis {(x)F,n:n0}\{(x)_{\downarrow_{F,n}}:n \geq 0\} and the Fibo-rising factorial basis {(x)F,n:n0}\{(x)_{\uparrow_{F,n}}:n \geq 0\} where (x)F,0=(x)F,0=1(x)_{\downarrow_{F,0}} = (x)_{\uparrow_{F,0}} = 1 and for k1k \geq 1, (x)F,k=x(xF1)(xFk1)(x)_{\downarrow_{F,k}} = x(x-F_1) \cdots (x-F_{k-1}) and (x)F,k=x(x+F1)(x+Fk1)(x)_{\uparrow_{F,k}} = x(x+F_1) \cdots (x+F_{k-1}). Then we study the combinatorics of the connection coefficients betweenthe usual power basis, the Fibo-falling factorial basis, and the Fibo-rising factorial basis. In each case, we can give a rook theory model for the connections coefficients and show how this rook theory model can give combinatorial explanations for many of the properties of these coefficients.

Keywords

Cite

@article{arxiv.1510.04310,
  title  = {A Fibonacci analogue of Stirling numbers},
  author = {Quang T. Bach and Roshil Paudyal and Jeffrey B. Remmel},
  journal= {arXiv preprint arXiv:1510.04310},
  year   = {2016}
}

Comments

Corrected typos and references