I'm not 100% sure if I'm doing it the right way, but I think the answer is the factorial of the number of letters divided by the factorials of the number of elements of each kind of element (in this case, the same letters)
9!/1!4!1!2!1!
= 9 · 8 · 7 · 6 · 5 · 4!/4!2!
= 9 · 8 · 7 · 6 · 5/2
= 9 · 4 · 7 · 6 · 5
= 63 · 120
= 7,560 permutations
