Let's say we have prime numbers p and q. p is the next prime number after q. The number of composite numbers in-between p and q are p-(q+1). Lets take p and say this is equal to TR(n). TR(n) is the first prime number after a group of composite numbers of length n or more. F(1)=TR(1)=5, F(2)=TR(TR(1))=29.
Uh so like capped around FGH level 3 or 4 [ These are only estimates. If you try copying this pattern after F(35) you get a number that is way smaller than the actual value. ]