二進指数え法
0
1
2
3 = 2 + 1
4
6 = 4 + 2
7 = 4 + 2 + 1
14 = 8 + 4 + 2
16
17 = 16 + 1
19 = 16 + 2 + 1
22 = 16 + 4 + 2
24 = 16 + 8
26 = 16 + 8 + 2
28 = 16 + 8 + 4
30 = 16 + 8 + 4 + 2
31 = 16 + 8 + 4 + 2 + 1