This is a system of counting that uses base 20 instead of 10.
1, 2, 3, 4, 5, 6, 7, 8, 9, !, @, #, $, %, &, ?, ~, <, >, 10...
= 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20...
A system of counting based on 3
1, 2, 10, 11, 12, 20, 21, 22, 30, 31, 32, 100, 101, 102, 110...
= 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15...
[n] means the actual definition of n is base 10
1 = [1]
2 = [2]
3 = [3]
4 = [4]
10 = [6]
11 = [7]
100 = [6!] = [720]
101 = [721]
102 = [722]
1000 = 720!
...