URL shortening function from https://github.com/briancray/PHP-URL-Shortener

shorten.php

<?php

/**
 * Generate a short URL based on an ID
 *
 * This function was lifted from: https://github.com/briancray/PHP-URL-Shortener
 *
 * @param  integer $integer The ID from which to generate the short URL
 * @param  string  $base    A string containing the set of characters used to construct the short URL
 *
 * @return string           The short URL
 */
function shortURL($integer, $base = '23456789abcdefghjkmnpqrstvwxyz') {
    $out    = '';
    $length = strlen($base);
    $base   = str_split($base);

    while ($integer > $length - 1) {
        $out     = $base[fmod($integer, $length)] . $out;
        $integer = floor( $integer / $length );
    }

    return $base[$integer] . $out;
}

$ids = array(1, 19, 287, 2076, 33043, 500032, 1786349);
foreach ($ids as $id) {
    printf('%d: %s' . PHP_EOL, $id, shortURL($id));
}