how much size of a column as identity?

Hi everyone,

I'm using Oracle version 12.

Are there methods that we can know how much size of a column as identity ?

Bellow is the sample script where UNIQUE_NUMBER is made as IDENTITY

CREATE TABLE TEST

   ( UNIQUE_NUMBER NUMBER(10,0) INVISIBLE GENERATED BY DEFAULT AS IDENTITY ORDER NOT NULL ,

     Column_1 NCHAR(6) DEFAULT ' ',

     ...

     PRIMARY KEY (UNIQUE_NUMBER)

    )

Thank you so much,