Working backwards, with the values you're getting from the division, result must be between 20,500 and 4,500. For an ADC result, this is absurd.
Instead of printing the result of the division, print the raw count value you're reading from the ADC. If it's not between 0 and 1023, you have a problem. (and if it is, that's even weirder).
However, you have only posted a snippet. It's good practice to post your FULL code in case the problem lies somewhere else.
How are you displaying this value?