Increment row values with some pre-defined values.

create table dummy
(
   [id] [int] identity(1,1) not null,
   [idwithchar] as ('p'+right('000'+convert([varchar](15),[id],0),(8))) persisted,
   [name] [nvarchar](25) not null,
    primary key clustered
   (
     [id] asc
    )with (pad_index = off,statistics_norecompute = off,ignore_dup_key = off,allow_row_locks = on,   allow_page_locks = on) on [primary]
) on [primary]

Note:- [idwithchar] will be treated as our Computed Column. 

insert into dummy values('vishal'),('neeraj kumar')
select * from dummy;