Formula

Determine the # of ways to get from (0,0) to (2,2) ..

I found it is 6 because of

(2,0) = 1
(2,1) = 3
(2,2) = 6
(2,3) = 10
(2,4) = 15
(2,5) = 21
(2,6) = 28

etc..

so who can give me a formula to explain this relationship for a general thing?

It seems to be But the thing is like delayed by 1. So