# Concept derivation guides

299 concept teaching guides, separate from the 36,000 individual question derivations.

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Concept guide



## [Counting phi(12) representative by representative](/en/derivations/derivation-mko-euler-totient-function-01/?from=%2Fen%2Fderivations%2F%3Fq%3Dmko-euler-totient-function)

phi(12)=4, phi(1)=1, and here phi(3*4)=phi(3)*phi(4).

Euler totient function

derivation-mko-euler-totient-function-01





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