When doing this for three mathematicians I follow the same logic that the last persons cookie count is neglectable.
0
0
10
0
1
9
0
...
...
0
10
0
These are the combinations for when the first person gets no cookies whatsoever. (still 11)
But when the first person gets a cookie the amount decreases by one. And for each cookie he(or she) gets the amount decreases...
1
0
9
1
1
8
1
...
...
1
9
0
Continue doing this until the first person gets 10 cookies and the rest none and I ended up with:
1+2+3+4+5+6+7+8+9+10+11. Or \(\sum_{i=1}^{11} i\)
I ended up looking through the case when there are four mathematicians(mostly seeing that depending on the value of cookies the first person had the combination count would be that sum, but 11 would decrease by each cookie the first mathematician had. So I set up the formula you can see in the post. At least that was my reasoning. I don't think N choose K applies here, sorry if I wasn't clear enough in my main post. I also sent you a pm, cheers :)