Along with their calendars -- the Tzolk'in, the Haab and the Long Count -- the Mayans also created their own math system. They used a series of dots and bars to signify numbers. One dot equaled one unit, while one bar equaled five units. A shell symbol signified zero.
In a system similar to the one we use now, the Mayans used place values to designate large numbers. However, the similarities between math systems end there.
Mayans' place values are vertical, whereas ours are horizontal. For instance, we write the number 27 horizontally -- the number two, then the number seven to the right of it. The Mayans, however, would write 27 vertically -- their symbol for seven (a line representing five units with two dots over it) would be on the bottom, and the symbol for 20 (a dot on the line above) would be directly over it. The same applies for other numbers, like 29.
Numbers held great significance in the Mayan culture. For example, the number 20 signifies the number of digits a person has -- 10 fingers and 10 toes. The number 13 refers to the major joints in the human body where it's believed disease and illness enter and attack: one neck, two shoulders, two elbows, two wrists, two hips, two knees and two ankles [source: Garcia]. The number 13 also represented the levels of heaven where sacred lords ruled the Earth [source: Tzolk'in Calendar].
It's these two numbers, 20 and 13, that are used to make up the Tzolk'in calendar, the first calendar used by the Mayans.