Geometric series?

Are you going through life with your eyes shut, or what? Anybody who uses a computer should know that those are computer numbers and the missing number is 128.

Look at a switch: it has two states, on and off, which we often write as zero and one.

Two switches have four states:
00
01
10
11

Three switches have eight states:
000
001
010
011
100
101
110
111

Every time you add a switch you double the number of states. A computer uses eight switches, called bits, so each group of eight bits can represent 256 combinations. Double a few more times and you get a list of computer numbers, which you will see quite often.

16
32
64
128
256
512
1024
2048
4096
8192
16384
32768
65536
and so on.