Aha! Found it! http://people.we.mediaone.net/kelsung/other/calendar/mayan.htm

The 13 numbers and 20 names cycle to produce the 260 day ritual calendar. This meshes with the 365 day calendar* to produce the 52 year cycle. This comes to 94,900 uniquely named days, given a name for each month and a number(?) for each day of the month.

*13 months times 28 days per month plus one day "out of time".