Published August 4, 2023 | Version v1
Journal article Open

Divisibility Properties for Integer Sequences

Authors/Creators

  • 1. Ohio State University

Description

For a sequence $f = (f_1, f_2, \dots)$ of nonzero integers, define $\Delta(f)$ to be the numerical triangle that lists all the generalized binomial coefficients 
\[ \abin{n}{k}_{f}  \;=\; \frac{f_nf_{n-1}\cdots f_{n-k+1}}{\!\!\!\!\!f_k\,f_{k-1}\phantom{i}\cdots\phantom{i} f_1}. \]
Sequence $f$ is called \emph{\bin} if all entries of $\Delta(f)$ are integers. For $I = (1, 2, 3, \dots)$, $\Delta(I)$ is Pascal's Triangle and $I$ is \bin.  Surprisingly, every row and column of Pascal's Triangle is also \bin.  
 For any  $f$, the rows and columns of $\Delta(f)$ generate their own triangles and all those triangles fit together to form the ``\Bim\ Pyramid'' $\bp(f)$.  Sequence $f$ is \emph{\bin\ at every level} if all entries of $\bp(f)$ are integers. 
We prove that several familiar sequences are \bin\ at every level.  For instance, every sequence $L$ satisfying a linear recurrence of order 2 has that property provided $L(0) = 0$.  The sequences $I$, the Fibonacci numbers, and $(2^n - 1)_{n \ge 1}$ provide examples.

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