Interesting. I would where that problem went! The problems just skip from 4.16 to 4.18. Good thing you only need to do 3 of the 4.
Although 4.17 Stutter isn't in the problem list, if you go to problem 4.16 printPalindrome, then you can click on 4.17 stutter's arrow at the top to get to 4.17 stutter.