Falling and rising factorials - Wikipedia

A frog jumps from the floor of an n-steps stair to the top of the stairs in k jumps, where k<=n.In how many different ways can the frog reach the top of

Why is n^k/k! not the correct number of ways to select k objects from n objects with replacement (order not important)? - Quora

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How to prove the factorial of 1/2 is 0.5√π - Quora

How to find all solutions to this set of functional differential equations? f'''…(x) = f(f(x)) for any derivative - Quora

What would be the value of n, when nP3=210? - Quora

Falling and rising factorials - Wikipedia

How many ways are there to climb the eight-step ladder if you always step on either one or two steps at a time? - Quora

Falling and rising factorials - Wikipedia

I had a question on a test, where I was supposed to subtract combinations in forms n choose k (binomial coefficients), the answers were also in forms n choose k, is there