Answer:
in each row it counts how many numbers are there individually.
Explanation:
for example in the first row there is the number 1
so, in the second row its says that there is one 1
in the third, it explains that in the previous row there is two 1's. in line four, it says 121 that explains the previous line, there is one 2 and one 1. And it goes on and on. so, for instance, in the last line, 111312112221, it explains that in the previous row, there is one 1, one 3, one 2, one 1, two 2's and two one's
