Genius Required?

Puzzles regularly appear on my time line in the form of a series of equations which purport to require a genius for their solution. Click here for one such puzzle

Despite the claims made by  whoever prepares these graphics, “that only a genius could solve them”,  the puzzles are typically trivial and would barely tax the abilities of an 11 year old in a high school maths class.

These puzzles invariably take me back more than forty years to a maths class I attended as a first year undergraduate student in Liverpool in 1969. The lecturer recounted a tale about a maths question, originally posed in an English eleven plus examination and subsequently put to Cambridge University mathematics undergraduates. According to the story the eleven year old kids had little difficulty but  none of the elite maths undergrads was able to answer the  question correctly.

Here is the question: what is the next number in the following series: 1/4, 1/2, 1, 3, 6.

I was the only one in my 1969 undergraduate class to get the correct answer, on the other hand I failed the 11+ exam.

Here is a clue: RTFQIHTFA

Let me know your proposed solutions to the puzzle ?

NOTE: the 11+ was an exam taken by British junior school kids to determine if they were smart enough to go to Grammar school or not*.  

*I wasn’t considered smart enough