Base 64 is a positional number system that uses 64 as a base. It is the greatest power of two that can be represented using only printable ASCII characters. This has led to its use for email encryption, PGP and other applications. All the famous variants known as Base64 use the character range AZ, az and 0-9 in this order for the first 62 digits, but the symbols chosen for the last two digits vary considerably from one to another. Other encoding methods such as UUEncode and the latest versions of binhex use a different set of 64 characters to represent 6 binary digits, but these are never called Base64.