the numeral 1 is just one one
one one can be written as 1 1
1 1 is actually two ones.
two ones can be written as 2 1
2 1 is one two and one one
one one and one two is 1 2 1 1
1 2 1 1 is one one, one two, and two ones.
one one, one two, and two ones is 1 1 1 2 2 1.
1 1 1 2 2 1 is three ones, two twos, and one one.
So the next number is 3 1 2 2 1 1.
It took me six months to solve (and a bit of help from some friends) ... shows you what kind of cryptologist I'd make!