and , where is a positive integer.
There are a positive integer number, , of independent vectors, , where runs from 1 to . A trip starts from the appropriate of components and goes to a destination vector of positive integer components. A step of a trip consists of adding to a single component of the taxi's current position vector which was initially of components. How many distinct routes would accomplish this trip?
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Look at Taxi trip counts #2 and see that the answer has to be 3 ! or 6.
Or, make a grid of points that is 2 by 2 by 2. This is one more than 1 because zero is included. Starting in one corner, label the points when all routes to the point are available with the sum of the ways to the point. Continue this process until the far corner is reached. If you did this correctly, then you will see the answer is 6.