Riyuna is playing with a two pan balance. There are N weights, one of each weight 21, 22, ⋯, 2N. Riyuna picks one weight that is not on the balance yet, puts it on the left pan or on the right pan, and repeats until all N weights are placed. Right after each placement, the total weight on the left pan must not exceed the total weight on the right pan.
Count the ways to place the weights. Two ways are the same only when the order of the weights is the same and every weight goes on the same pan in both.