This property defines the Unicodes which have numeric value as 21
Characters like ㉑, etc. are listed under 21 Numeric Value.
1 Characters are present in 21 Numeric Value starting with the Unicode point U+3251 that represents the character ㉑.
Currently, as per latest version 15.0.0, Unicode supports 150 number of Numeric Value. Here are a few examples - 0,1,1/10, etc.