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Definition df-phi 10966
Description: Define the Euler phi function (also called _ Euler totient function_), which counts the number of integers less than 𝑛 and coprime to it, see definition in [ApostolNT] p. 25. (Contributed by Mario Carneiro, 23-Feb-2014.)
Assertion
Ref Expression
df-phi ϕ = (𝑛 ∈ ℕ ↦ (♯‘{𝑥 ∈ (1...𝑛) ∣ (𝑥 gcd 𝑛) = 1}))
Distinct variable group:   𝑥,𝑛

Detailed syntax breakdown of Definition df-phi
StepHypRef Expression
1 cphi 10965 . 2 class ϕ
2 vn . . 3 setvar 𝑛
3 cn 8315 . . 3 class
4 vx . . . . . . . 8 setvar 𝑥
54cv 1284 . . . . . . 7 class 𝑥
62cv 1284 . . . . . . 7 class 𝑛
7 cgcd 10717 . . . . . . 7 class gcd
85, 6, 7co 5590 . . . . . 6 class (𝑥 gcd 𝑛)
9 c1 7253 . . . . . 6 class 1
108, 9wceq 1285 . . . . 5 wff (𝑥 gcd 𝑛) = 1
11 cfz 9318 . . . . . 6 class ...
129, 6, 11co 5590 . . . . 5 class (1...𝑛)
1310, 4, 12crab 2357 . . . 4 class {𝑥 ∈ (1...𝑛) ∣ (𝑥 gcd 𝑛) = 1}
14 chash 10017 . . . 4 class
1513, 14cfv 4968 . . 3 class (♯‘{𝑥 ∈ (1...𝑛) ∣ (𝑥 gcd 𝑛) = 1})
162, 3, 15cmpt 3865 . 2 class (𝑛 ∈ ℕ ↦ (♯‘{𝑥 ∈ (1...𝑛) ∣ (𝑥 gcd 𝑛) = 1}))
171, 16wceq 1285 1 wff ϕ = (𝑛 ∈ ℕ ↦ (♯‘{𝑥 ∈ (1...𝑛) ∣ (𝑥 gcd 𝑛) = 1}))
Colors of variables: wff set class
This definition is referenced by:  phival  10968
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