Count to 20 in binary, and explain the pattern you see developing as the numbers go up.
1
10
11
100
101
110
111
1000
1001
1010
1011
1100
1101
1110
1111
10000
10001
10010
10011
10100
10101
10111
11000
11001
11010
11011
11100
11101
11110
11111