Arabic numerals were adopted. I am still rather unsure, but I did rediscover something I haven't thought about for years (I have random memories of researching for an art and math paper in junior college, and seeing this in the electronic periodical records): Sangaku.
Shrines have little evocative wooden tablets; usually prayers, wishes, and horses adorn them. But Sangaku were euclidean-geometry puzzles painted onto such tablets, and set out for those merry 参る者* to solve.
Most of them seem to involve circles. But anyway, here are some examples, and here is a concise history with good insights into the cultural background.
Also, this is at a shrine in Fukuoka; I want to find it, but it is from 1984(?) with Arabic numerals.
*:totally just made up a term for shrine-goer.