fareylen
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## fareylen

fareylen — returns the length of a Farey Sequence.

## Description

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

## Syntax

    kfl fareylen kfn

## Performance

The length of the identified Farey sequence is returned.

kfn -- Integer identifying the sequence.

## Credits

Author: Georg Boenn
University of Glamorgan, UK

New in Csound version 5.13

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