The system of Japanese numerals is the system of number names used in the Japanese language, and its forms evolved as the language evolved.
“The native system of numerals is simple and partly based on vowel alterations to show doubling: pito ‘1’~puta ‘2’; mi ‘3’ ~ mu ‘6’; yo ‘4’ ~ ya ‘8’.
However, the system does not provide easily for formation of higher numbers … Some SJ numbers were used in OJ … But the intake of SJ numerals is usually thought not to have taken place until EMJ.
The Japanese numerals in writing are almost entirely based on the Chinese numerals and the grouping of large numbers follow the Chinese tradition of grouping by 10,000. For most purposes today, the Chinese number system is used, rather than native numbers. However, native numbers are often used for counting numbers of items up to 10 – as in hitotsu, futatsu, mittsu (one item, two items, three items), notably days on the calendar, and with other Japanese counter words – and for various exceptions (fossils). These exceptions include 20 years old (hatachi), the 20th day of a month (hatsuka), 八百屋 (yaoya, greengrocer, literally “800 store”), and 大晦日 (ōmisoka – last day of the year, literally “big 30th day”)…see The Number System of the Ancient Japanese.
Origin of the number systems
The origin of the earlier ‘native ‘ number system is obscure, scholars attribute it to various Uralic-Altaic/Finno-Ugric/Melanesian sources, but so far clear evidence and proof is lacking. See Stefan Tanaka’s summary of earlier theories on the origins of the native counting system, including Shiratori’s that:
“…placed them within the Ural-Altaic family. the Ainu language, though monosyllabic like the languages of Southeast Asian cultures, provided, he said, objective proof of a Ural Altai affinity, for it exhibited agglutination like some Ural-Altaic affinity, for it exhibited agglutination like some Ural-Altaic languages, particularly Finn-Ugri and Samoyed, and also a similarity in the basic construction of some numbers, especially six through nine.”
“…The original numerical system, he suggested was based on a reduplicative scheme that was in turn reflected in the counting system. ancient Japanese used two hands to count: two (puto) was formed by adding one (pito) finger on one hand to the identical one on the other hand; three (mi) doubled to six (mu); four(yo) doubled to eight (ya); and five (it) doubled to ten(to)..”–Japan’s Orient: Rendering Pasts Into History by Stefan Tanaka
The task of tracing the origin of the Chinese number system, however, is more productive, and strong similarities can be seen in the number system adopted in ancient Japan with those used by the earliest Sino-Tibetan tribes…see the closest cognates charted below:
Japanese English Proto-Sino-Tibetan Written Tibetan/ Tibetan /Kannauri
ichi ONE*ʔit / *kat / *tjak ~g-t(j)ik. geig / cheek. / id
ni TWO*g/s-ni-s gnis / nyee / nis
san THREE*g-sum gsum/ soom / sum
yon/shi FOUR*b-ləj bzi / zhee / pu
go FIVE*l/b-ŋa lgna / nga /ga
roku SIX*d-(k-)ruk drug/ drook / kuk
shichi SEVEN*s-ni-s bdun / dun / stif
hachi EIGHT*b-r-gjat ~ b-g-rjat brgyad / gyay / rai
ku1/kyū2 NINE*d/s-kəw dgu / goo / zgui
1) From Early Middle Chinese Goon, the initial reading when first borrowed into Japanese
2) From Middle Chinese Kan’on, a later reading. Borrowed after palatalisation occurred in Middle Chinese.
juu TEN*gip / *tsi(j)i(j) ~ tsjaj bcu / choo / sai
Further comparative sources and references:
Korean counting system (non-native, Sino-Korean):
1-Il 2-i 3-sam 4-sa 5-o 6-yuk 7-chil 8-pal 9-gu 10-ship
The above system is close to the Hakka counting system (below)
1-jit 2-ngi 3-sam 4-si 5-ng 6-liuk 7-cit 8-bat. 9-giu 10-siip
Ainu counting system:
1-sirep 2-tup 3-rep 4-inep 5-asiknep 6-iwanpe 7-arwampe 8-tupesanpe 9-sinepesanpe 10-wanpe 20-hotnep 100-asikne hotnep
Source: Systems of the world
Mongolian counting system:
1 – neg. 2 – hoyor. 3 – guraw. 4 – doruw. 5 – tav. 6 – zurgaa 7 – doloo. 8 – naym. 9 – yes. 10 – araw
1-Nigen 2-Qoyar 3-rurban 4- Dorben 5 -Tabun 6-Jiryuyan 7-Doloyan 8-Naiman 9-Yisun 10-Arban
1-Ib 2-ob 3-Peb 4-Plaub 5-Tsib 6-Rau 7-Xya 8 – Yim 9-Cuaj 10 – Kaum
Sino-Tibetan numerals and the play of prefixes
Volume 86 1977 > Volume 86, No. 1 > Kapauku numeration: reckoning, racism, scholarship, and Melanesian counting systems, by Nancy Bowers, p 105-116
Indo-European Numerals by Jadranka Gvozdanović