1, in case the mouse strays off the top
1, A
4, B
5, C
9, D
10, E
11, F
12, G
13, H
14, I
15, J
15, K
15, L
16, M
17, N
18, 0
18, PQ
19, R
21, S
24, T
26, U
26, V
27, W
28, X
28, YZ
28, in case the mouse strays off the bottom