You'll never get this unless you heard it before!

I notice that the last line contains "one three, one one,....."

lol they do this in my class constantly i've seen like millions of em here's another version:

7
17
1117
3117
132117
1113122117
311311222117
13211321322117
.
.
.

Notice that the original number (7 in this case) is always at end.

by the way, 1113213211 is the next number in the sequence

Brains riddle is more related to grammar than math.

Not for blain's riddle.