A discrete mathematics problem by TheKnee OfJustice
Along a one-way street there are 10 parking lots. One after another, 10 cars numbered 1-10 enter the street. Each driver i heads to his favorite parking lot ai, and, if it is free, takes it. If not, he continues to the parking lot directly after that, and if that is occupied, then he continues to the parking lot after that... and if he finds that he gets to the 10th parking lot in this way, and it is occupied, then he just exits the street and therefore doesn't park. How many sequences ai are there such that every driver parks on the street. (Two cars cannot park in the same parking lot, and a parking lot just means a space where a car can park). Sorry, this is very embarrassing. I believe that I typed the answer wrong when I was answering the problem. From you answer, take the second digit from the right (e.g. if the answer is 13579-it's not-, then take 7, now add a 1 before that, so 13579 becomes 135179). Or, someone could tell me how to edit solutions.