Arithmetic overflow error converting expression to data type datetime. (while displaying date time..)

Arithmetic overflow error converting expression to data type datetime.
(while displaying date time..)

While executing following error is showing
declare @yr_mnth_dt as numeric;
set @yr_mnth_dt = 20130822;
select convert(datetime,@yr_mnth_dt,112) as YR_MNTH_DT
error shows
Arithmetic overflow error converting expression to data type datetime.