Can you define the parameters of this problem a little more?
Are they entering all the numbers into a single entry box? Are they entering one then saving then entering the next then saving, so on and so forth?
In order to have the server initiate a user prompt you need to emit javascript that performs the prompting (i.e. using an alert box) then save the response from the client to some server control (most likely a hidden form element) then initiate a postback on the client side. This can be a bit more challenging than just showing a prompt in the page text with the appropriate response buttons as server-side buttons. Alternatively you could do all of this on the client side, but then you have to ensure that your javascript works in the browser environments you want to support and you should also provide server-side checking to eliminate client-side circumvention of the checks.
-Peter
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