seems to be a port of the ruby version which is pretty straight forward ported for a Perl hacker

http://gist.github.com/jonelf/3423148

update

Basically it's a inductive solution building complex sequences from more primitive ones starting with (1,1).

I'm sure porting to Perl, using longer var names and dumping part solutions would explain the idea.

update

Though finding the original article would be better.