If I do this in sage
F=sum(k^2*factorial(n), v=k, a=1, b=n+1); F
it correctly expands to what I want:
⎛ 3 2 ⎞
⎝2⋅n + 9⋅n + 13⋅n + 6⎠⋅n!
───────────────────────────
6
However, if the factorial is a function of the summed variable, it doesn't work anymore:
sage: F=sum(k^2*factorial(k), v=k, a=1, b=n+1); F
sum(k^2*factorial(k), k, 1, n + 1)
sage: F.expand_sum()
sum(k^2*factorial(k), k, 1, n + 1)
Is this the expected behavior? How can I get it to expand no matter what's inside the summation?
I'm using Sagemath 7.5, by the way.
Thank you.
