1

1/2 1/2

1/3 1/6 1/3

1/4 1/ 12 1/ 12 1/4

1/5 1/20 1/30 1/20 1/5

1/6 1/30 1/60 1/60 1/30 1/6

It can be found that the sum of every two adjacent numbers is the top number.

For example: 1/2+ 1/2= 1.