# falling_factorial produces AttributeError

Mathematica:

`Table[FactorialPower[n, n - k - 1], {n, 0, 5}, {k, 0, n}] {{1}, {1, 1/2}, {2, 1, 1/3}, {6, 3, 1, 1/4}, {24, 12, 4, 1, 1/5}}`

Maple:

`ff := (n,k) -> n!/(n-k)!: for n from 0 to 5 do seq(ff(n, n-k-1), k=0..n) od; 1 1, 1/2 2, 1, 1/3 6, 3, 1, 1/4 24, 12, 4, 1, 1/5`

Sage:

`for n in range(6): [falling_factorial(n, n-k-1) for k in (0..n)] AttributeError: 'int' object has no attribute 'parent'`