The next letter in the row?

[Weird]

Can somebody give me the next letter in the following row "OTTFFSS" with a correct reasoning, because I also just guessed it right (first try) but before I tried god knows which mathematical rows on paper...?

What a sick registration question, what kind of community is this? The "Mensa Club"?

Uiuiuiui :D

[Weird]

I googled it now... answer is boring