As in, if you had this number sequence:

1

If you read it phonetically, you would say, "One 1", or for the next line you would have:

11

Again, read it photenically, you would say, "Two 1's", or for the next line you would have:

21

So on and so forth...

1211
111221
312211
13112221
1113213211
31131211131221
13211311123112112211
etc., etc. etc...