php输出打印0500

I have following php code.

    <?php
           print 0505;
           echo "
";
           print 0500;
     ?>

output =>   325
            320

can anyone tell me how come did this output?

0x*** - hex number (16)
0b*** - bin number (2, PHP5.4)
0*** - oct number (8)
*** - dec number (10, normal)

This is octal

Here is a octal/decimal converter.

500 oct = 320 dec

505 oct = 325 dec

You can get output using this format

print "0505";

echo " ";

print "0500";

Because this is octal/decimal convertor