They are the initial letters of the numbers 0-7 in words: Zero, One, Two, Seven
The next is 8 - Eight
The question is stated wrong.It should be: "What is the next letter in the series O T T F F ?", and the answer is " S ".These are the initial letters of the words: One Two Three Four Five, followed by Six.
It looks as if every third letter is an "r"; the remaining letters are in sequence.
oNe, tWo, tHree, fOur,fIve,sIx etc. It is the second letter of each consecutive number
The pre-penultimate element of the series.
what is the next letter e h l q
c is next
The next (and last) letter is C. Just as a countdown counts backwards, this series is "countdown" spelled backwards.
It's the letter D of course! Haven't you heard of Jason D?!