Class 9ᵗʰ student, Mahi visits the bank for the first time along with her…

Class 9ᵗʰ student, Mahi visits the bank for the first time along with her father. She observes that father is issued with a small book which her father tells that it is a cheque book. She opens it and finds some pre-printed information on it. Some of the information printed is same on all the pages but one number is printed in a serial order. She tries to change it. But she is unable to do it. Why she is not able to change it? Identify the specialised feature of the cheque.