You are looking for the LARGEST numeral—when written out—that has 9 letters in it, so it would be “96.” (“17,” when written out, also has 9 letters, but it is the smallest numeral.)
“ten, nine, sixty, ninety, seventy, sixty-six, ninety-six” is an acceptable answer, but ninety-six is not exactly the largest number with nine characters. Maybe you stopped before one hundred because it requires ten characters and up.
The best response can actually be traced back to 1938 or thereabouts. Let me know if you want another hint.
Augmental 
No “number” comes next.
All of these are “numerals”—which represent the concept of a number.
Good point, Eddie.
I’ve revised the question to cover both bases, the distinction being that a “number” is an idea, whereas the “numeral” is how that idea is expressed.
In any case, there is a blank to be filled in that logically answers the question.
Can you figure it out?
-Gary
Hint: Writing out the numbers on paper is a big, perhaps essential, help.
The next “number” in this series is 17.
Thank you for this challenge. I appre-she-ate it.
Keep ’em comin’.
In peace . . .
“17” is incorrect.
You are looking for the LARGEST numeral—when written out—that has 9 letters in it, so it would be “96.” (“17,” when written out, also has 9 letters, but it is the smallest numeral.)
Sew sari . . .
“ten, nine, sixty, ninety, seventy, sixty-six, ninety-six” is an acceptable answer, but ninety-six is not exactly the largest number with nine characters. Maybe you stopped before one hundred because it requires ten characters and up.
The best response can actually be traced back to 1938 or thereabouts. Let me know if you want another hint.
Instead of “ninety-six,” the largest number with nine characters is “ten googol.”
Is it googleplex?
Very good answer, Lawrence.
-Gary