Saraveca language

Saraveca is an extinct Arawakan language once spoken in Bolivia by the Sarave. By 1962, most people has switched to Chiquitano.

It is said to be the only language with a numeral system based exclusively on five, although quinary systems exist. To some extent this is also an areal feature of other South American languages; many form their numbers 6–9 as "five + one", "five + two" and so on.