How does that work? Like this? That's not really following the "pattern" though, which is to keep adding 1 down the left edge of the triangle. Choosing to put a 0 in because we ran out of terms in our series is pretty arbitrary.

    1  2  4  8 16 31
     1  2  4  8  15
       1  2  4  7
        1  2  3
          1  1
           0