Numbered musical notation
The numbered musical notation (simplified Chinese: 简谱; traditional Chinese: 簡譜; pinyin: jiǎnpǔ; lit. 'simplified notation', not to be confused with the integer notation) is a cipher notation system popular in mainland China, Taiwan and Hong Kong and with the Chinese diaspora in other countries; a variant used in Indonesia is called "not angka".
Source: Wikipedia — Numbered musical notation (CC BY-SA 4.0)