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Math and science::Algebra::Aluffi

Euler's ϕ

Euler's ϕ-function

Euler's ϕ-function maps any positive integer m to the number of [what?]. In other words:

[ ϕ(m)=|{r∈N:?}| ]

A related theorem:

Theorem. N = sum of relative primes of divisors of N.

∑m>0,m|nϕ(m)=n

Proof is on the reverse side.