num_factor

num_factor 
      ::= 
      ( numeric_literal 
      | variable_name 
      | host_variable 
      | ( function [ "(" plsql_exp_list ")" ] ) 
      | ( "(" num_expression ")" ) 
      | "null" 
      | ( ( cursor_name | subquery ) "%rowcount" ) 
      ) [ "**" integer_expr ] 

This rule is call by

-> num_term