Here’s a little puzzle:

There exists a function ƒ(n) which takes a natural number n as an argument and returns a character.

It can be said with certainty that natural numbers smaller than 20 are in ƒ’s domain.

ƒ(n) for the first 15 values of n is exhibited in the image below, in the following order:

ƒ(1) ƒ(2) ƒ(3) ƒ(4) ƒ(5)
ƒ(6) ƒ(7) ƒ(8) ƒ(9) ƒ(10)
ƒ(11) ƒ(12) ƒ(13) ƒ(14) ƒ(15)



Click here for large size image


Define ƒ.
Estimate the domain of ƒ.



Hint:

Here is a dictionary.


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