3 letters is 1 (one)
4 letters is 0 (zero)
5 letters is 3 (three)
6 letters is (?)
7 letters is (?)
8 letters is (?)
9 letters is (?)
10 letters is (?)
15 letters is 103 (one hundred three ^*)
20 letters is (?)
25 letters is (?)
30 letters is (?)
40 letters is (?)
50 letters is (?)
100 letters is (?)

In the above list replace all interrogation marks by a correct answer.

^* Note the absence of the word "and".