Lock Combination Calculator Math Problem- Permutations: Combination Lock?

Math problem- permutations: combination lock? - lock combination calculator

A combination lock is opened when the correct choice of three numbers (1-40, is selected included). How many different combinations are possible barriers?

The answer is 64000, but when I plug into the computer as is 4P3 59,280. What am I doing wrong?

I have tried to do is possible even 40 x 39 x 38 (the first three questions), and then I have 59,280.

Moreover, what is integration?