Finds the largest palindromic number that is the product of two 3-digit numbers

FactorFinder.php

<?php
/**
 * User: frank.steinberg
 * Date: 7/30/18
 * Time: 11:57 AM
 */

class FactorFinder
{
    public function run()
    {
        $currentPalindromicNumber = 997799;
        while ($currentPalindromicNumber >= 100001 ) {
            $currentPalindromicNumber = $this->getNextPalindromicNumber($currentPalindromicNumber);
            $factors = $this->getThreeDigitFactors($currentPalindromicNumber);
            if ($factors) {
                echo join(' x ', $factors) . ' = ' . $currentPalindromicNumber . PHP_EOL;
                return $currentPalindromicNumber;
            }
        }

        echo "Could not find 3-digit factors that created a palindromic number when multiplied." . PHP_EOL;
    }

    public function getNextPalindromicNumber($lastPalindromicNumber)
    {
        $convertToInt = function($value) {
            return (int) $value;
        };

        $digits = array_map($convertToInt, str_split((string) $lastPalindromicNumber));;
        if ($digits[2] > 0) {
            $digits[2]--;
            $digits[3]--;
            return (int) (join('', $digits));
        }

        $digits[2] = 9;
        $digits[3] = 9;
        if ($digits[1] > 0) {
            $digits[1]--;
            $digits[4]--;
            return (int) (join('', $digits));
        }

        $digits[1] = 9;
        $digits[4] = 9;
        if ($digits[0] > 0) {
            $digits[0]--;
            $digits[5]--;
            return (int) (join('', $digits));
        }
    }

    public function getThreeDigitFactors($n){
        for ($factor1 = (int) sqrt(abs($n)); $factor1 >= 100 ; $factor1--)
        {
            if (
                $n % $factor1 == 0
                && ($factor2 = $n / $factor1) <= 999
            ) {
                return [
                    $factor1,
                    $factor2
                ];
            }
        }
        return null;
    }
}