Oooh Cool. Math Bragging by "White Chested Fox" (Sak Tahn Waax), ca 800AD:

   The formula shows how one 2,920-day cycle could be divided up into the calendar units used by the Maya people. This 2,920-day cycle was important because it tied together key astronomical cycles, corresponding to both five Venus cycles (584 days each) and eight solar years (365 days each). However, the Text 19 calculations also relate the 2,920 days to Uinal (months with 20 days), Tzolkin (the 260-day sacred calendar), Tun (a year with 360 days) and Mars years of 780 days.