Pascal's triangle

      ∘.!⍨ ⍳12
1 1 1 1 1  1  1  1  1   1   1   1
0 1 2 3 4  5  6  7  8   9  10  11
0 0 1 3 6 10 15 21 28  36  45  55
0 0 0 1 4 10 20 35 56  84 120 165
0 0 0 0 1  5 15 35 70 126 210 330
0 0 0 0 0  1  6 21 56 126 252 462
0 0 0 0 0  0  1  7 28  84 210 462
0 0 0 0 0  0  0  1  8  36 120 330
0 0 0 0 0  0  0  0  1   9  45 165
0 0 0 0 0  0  0  0  0   1  10  55
0 0 0 0 0  0  0  0  0   0   1  11
0 0 0 0 0  0  0  0  0   0   0   1

Each entry is the sum of the one left of it and the one above and left.