For a person with normal (not absolute pitch) hearing ( and for the purpose of the Copyright Law), the key of the melody is immaterial. This immediately reduces your estimate by a factor of 12. Furthermore, most (>99% ?) series of random pitch jumps would not be considered a melody but a cacophony. I suspect the actually number of possible "ear-pleasing" melodies is within reach of one generation of 5 bln. people. Soon , we will be hearing mostly recycled music. And it's OK, since copyrights do not last forever.