How to create autogen no in sql server

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SQL-Server-2005

SQL-Server

Hello

I have create a query for creating auto generate no i.e:

select  row_number() over(order by O.Col_Id) as SlNo,  O.Col_Date,Account_No,Scheme_Name,O.Col_No,Instalment_Amount,O.No_Of_Instalment,O.Col_Amount ,Permanent_Address,
 (select sum(Col_Amount) from t_Customer_Deposit where Col_Id <= O.Col_Id and Col_Customer_Id=1) as 'Running_Total'
 from t_customer_account inner join t_customer_deposit O on t_customer_account.customer_id=O.col_customer_id inner join
 t_scheme_master on t_customer_account.scheme_id=t_scheme_master.scheme_id where customer_id=1

It is creating auto generate no and working fine but i want to create, after completion of 20 record the slno will start from 1.

If any solution then please help me.
Thanks