Alphabetic Puzzle

[Naresh]

O T T F F S S E N _
What will come in this blank?

[koolz]

My answer - T - Ten

[Naresh]

My answer - T - Ten

Please explain with logic

[Vivek]

O T T F F S S E N _
What will come in this blank?

OTTFFSSEN .....T.......

One , Two , Three , Four , Five , Six , Seven , Eight , Nine .....Ten.