What is the next letter in this riddle?

o t t f f s s _ _

It's "e".....

One
Two
Three
Four
Five
Six
Seven

Then comes "e" for eight and "n" for nine.

Hope this helps. :)

The sequence in this riddle follows a pattern where each letter represents the number of letters in the corresponding number word.

- The word "one" has 3 letters, so the first letter of the sequence is "o".
- The word "two" has 3 letters, so the second letter of the sequence is "t".
- The word "three" has 5 letters, so the third letter of the sequence is "t".
- The word "four" has 4 letters, so the fourth letter of the sequence is "f".
- The word "five" has 4 letters, so the fifth letter of the sequence is "f".
- The word "six" has 3 letters, so the sixth letter of the sequence is "s".
- The word "seven" has 5 letters, so the seventh letter of the sequence is "s".

By following this pattern, we can determine that the next number in the sequence, representing the word "eight," has 5 letters. Therefore, the missing letter in the sequence is "e".