Problem Four

four.php

for ( $i = 998001; $i >= 10000; $i-- ) {
    
    // Cast as string and calculate length;
    $test = (string) $i;
    $length = strlen( $test );

    // Check if we have a the first part of a palindromical number
    if ( ! ( $test[0] === $test[ $length - 1 ] && $test[1] === $test[ $length - 2 ] ) )
        continue;
        
    // If it's a 6 digit number and palindromical or if it is 5
    if ( ! ( $length === 6 && $test[2] === $test[ $length - 3 ] || $length === 5 ) )
        continue;
            
    // Check if the number has a factor
    if ( has_factor( $test ) ) {
        echo $test;
        break;
    }
        
}


function has_factor( $product ) {
    
    for ( $d = 100; $d <= 999; $d++ ) {

        if ( $product % $d !== 0 )
            continue;

        $divisor = $product / $d;

        if ( $divisor >= 100 && $divisor <= 999 )
            return true;

    }
    
    return false;

}