The Nahuatl system has quinary and decimal features up to 20, but
beyond that the units named with specific lexical items are multiples of
20:
20 is <cempo:hualli> = cen- "one" + po:hualli "count, something
counted"
400 is <centzontli> = cen- "one" + tzontli, literally, "bundle of feather
barbs"
8000 is <cenxiquipilli> = cen- "one" + xiquipilli, literally "sack (of cacao
beans or the like)"
To the best of my knowledge all other languages in the Mesoamerican
cultural area (Mayan, Mixe-Zoque, the very large Otomanguean family,
numerous small families and isolates) have comparable systems.
Jim Rader
>
> Not so much its use as its origin and spread in Europe. '20' is a
> natural kind of base, like '10' and '5'. Systems with vigesimal
> features are found e.g. in Central America. I doubt, however, if there
> are any _strictly_ vigesimal systems anywhere -- in all the cases
> known to me we have basically quinary or decimal systems with '20' as
> an auxiliary base.
>
> Piotr
>