Dzongkha, the national language of Bhutan, has two numeral systems, one vigesimal (base 20), and a modern decimal system. The vigesimal system remains in robust use. Ten is an auxiliary base: the -teens are formed with ten and the numerals 1–9. Ex. cu_ci
Vigesimal
*When it appears on its own, 'ten' is usually said 'a full ten'. In combinations it is simply .
Multiples of 20 are formed from . Intermediate multiples of ten are formed with 'half to':
400 (20²) is the next unit: 400, 800, etc. Higher powers are 8000 (20³) ('a ɡreat score') and 160,000 (20⁴).
Decimal
The decimal system is the same up to 19. Then decades, however, are formed as unit–ten, as in Chinese, and the hundreds similarly. 20 is reported to be , the same as vigesimal numeral 400; this may be lexical interference for the expected . (In any case, there is no ambiguity, because as 400 it is obligatorily 'one 400'.) Several of the decades have an epenthetic , perhaps by analogy with 18 and 19, where the presumably reflects a historical 'ten':
30, 40, 50, or 100 (a 'full hundred' or 'one hundred'), 200, 300, 400, etc.
References
Mazaudon & Lacito, 2002, "Les principes de construction du nombre dans les langues tibeto-birmanes", in François, ed. La Pluralité, p. 6 ff