What core clocks ( mhz ) have a 21.3 memory bandwidth ( gb/s )?
create table table_25839957_5 (core_clock___mhz__ varchar, memory_bandwidth___gb_s__ varchar, PRIMARY KEY (core_clock___mhz__))
select core_clock___mhz__ from table_25839957_5 where memory_bandwidth___gb_s__ = "21.3"