fareylen — returns the length of a Farey Sequence.
This opcode can be used in conjunction with GENfarey. It calculates the length of Farey Sequence Fn. Its length is given by: |Fn| = 1 + SUM over n phi(m) where phi(m) is Euler's totient function, which gives the number of integers ≤ m that are coprime to m.
Some values for the length of Fn given n:
| n | Fn | 
|---|---|
| 1 | 2 | 
| 2 | 3 | 
| 3 | 5 | 
| 4 | 7 | 
| 5 | 11 | 
| 6 | 13 | 
| 7 | 19 | 
| 8 | 23 | 
| 9 | 29 | 
| 10 | 33 | 
| 11 | 43 | 
| 12 | 47 | 
| 13 | 59 | 
| 14 | 65 | 
| 15 | 73 | 
| 16 | 81 | 
| 17 | 97 | 
| 18 | 103 | 
| 19 | 121 | 
| 20 | 129 |