TADM2E 2.33

On careful observation , one can see that the sum of any row is just $ 3^n $ this is the sum for the series . This can even be computed using a series as shown below

1=a0
1 1 1 
a1 a0 a2

now a(mid) of the next line becomes the a(0) +a(1) +a(2) that it this mid element is always the sum of the middle three elements