strin base_convert(string number, int frombase, int tobase);
Returns a string containing number represented in base tobase. The base in which number is given is specified in frombase. Both frombase and tobase have to be between 2 and 36, inclusive. Digits in numbers with a base higher than 10 will be represented with the letters a-z, with a meaning 10, b meaning 11 and z meaning 36.
Example 1. base_convert()
$binary = base_convert($hexadecimal, 16, 2);