On Polynomial Pairs of Integers

Abstract

The reversal of a positive integer $A$ is the number obtained by reading $A$ backwards in its decimal representation. A pair $(A,B)$ of positive integers is said to be palindromic if the reversal of the product $A\times B$ is equal to the product of the reversals of $A$ and of $B$. A pair $(A,B)$ of positive integers is said to be polynomial if the product $A\times B$ can be performed without carry. In this paper, we use polynomial pairs in constructing and in studying the properties of palindromic pairs. It is shown that polynomial pairs are always palindromic. It is further conjectured that, provided that neither $A$ nor $B$ is itself a palindrome, all palindromic pairs are polynomial. A connection is made with classical topics in recreational mathematics such as reversal multiplication, palindromic squares, and repunits.

13 pages, 3 tables, errors are corrected, some proofs are made more explicit