Are numbers part of romaji? (i.e. 1, 2, 3 vs 一二三)

Question

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.

Answer 1

They are known as Arabic Numerals, or アラビア数字 in Japanese. As you may notice, 1, 2, 3, etc. were developed by Indian mathematicians and did not originate from ancient Rome. Up until the 14th century Roman numerals were used, but were eventually abandoned in favor of Arabic Numerals.

Answer 2

As Jesse Good said, Arabic numerals (0, 1, 2, …, 9) are called アラビア数字 in Japanese. Another name for them is 算用数字.

As an aside, numerals in kanji (一, 二, 三, …), loaned from Chinese, are called 漢数字 in Japanese. Roman numerals (I, II, III, …) are called ローマ数字.