How do you write 81 in Japanese?

Answer 1

八十四 (hachi-juu yon) would be "84" in Japanese. Literally what is being said is "eight-ten four" and you may realize from this that the Japanese actually use this stylistically throughout the rest of their numbering system. So from here it should be easy to see why 九十七 (kyuu-juu nana) is "97" or 三百五十六 (san-byaku go-juu roku) is "356".

Answer 2

It can be written　八十一