Romaji is when you use the Roman alphabet to write out Japanese. I.e. you use "abc" instead of "あいうえお". Taking that one step further, what do you call it when you use "123" instead of "一二三"? My first thought was to call it "Roman numerals", but those are "I, II, III"...so would they be "Romaji numbers"? I realize usually we would just call them "numbers" in English (and in Japanese "数字"), but there is there a way to call them when there is a need to differentiate them?
The reason why I'm asking is because I was reading a book, and someone's age was written out in kanji numbers, and it got me thinking.