Brain Teaser

What would be the seventh rung of the following pyramid?
1
11
21
1211
111221
312211
13112221

Here is the correct answer

Answer: 1113213211. After the first line, each line describes the previous line as follows:
one 1
2 Ones
One 2, One 1
(and so on...)

1 is read off as "one 1" or 11.
11 is read off as "two 1s" or 21.
21 is read off as "one 2, then one 1" or 1211.
1211 is read off as "one 1, then one 2, then two 1s" or 111221.
111221 is read off as "three 1s, then two 2s, then one 1" or 312211.