Assign the number of ways to share 16 identical objects

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In how many different ways can be shared 16 identical objects to 7 different persons such that 3 of them can accept maximum of 2 objects, 3 of them at least 2 objects and for the other person don't have restriction. I don'n know if I'm on the right way but I started like this: f(x)= (1+x+x^2)^3 (x^2+x^3+...+x^16)^3 (1+x+x^2+x^3+...+x^16) then the number of ways is the coefficient of x^16.

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You can just give two to each of the three that needs at least two, then distribute the remaining $10$ to ease the restrictions. That removes the overall factor $x^6$ from your expression. Your approach is fine, but this makes the maximum exponent $10$ which simplifies things a bit. You can also extend the sums to infinity because powers above $10$ will not matter. Then you get $(1+x+x^2)^3(\frac 1{1-x})^4$ and you are looking for the coefficient of $x^{10}$. Alpha says the answer is $3483$. You may have to click on More Terms to see it.