Difference between revisions of "Euler's totient function"
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The formal definition is <math>\phi(n):=\# \left\{ a \in \mathbb{Z}: 1 \leq a \leq n , \gcd(a,n)=1 \right\} </math>. | The formal definition is <math>\phi(n):=\# \left\{ a \in \mathbb{Z}: 1 \leq a \leq n , \gcd(a,n)=1 \right\} </math>. | ||
| − | Given the [[prime factorization]] of <math>{n} = {p}_1^{e_1}{p}_2^{e_2} \cdots {p}_n^{e_n}</math>, | + | Given the [[prime factorization]] of <math>{n} = {p}_1^{e_1}{p}_2^{e_2} \cdots {p}_n^{e_n}</math>, one can compute <math>\phi(n)</math> using the formula <math> \phi(n) = n\left(1-\frac{1}{p_1}\right)\left(1-\frac{1}{p_2}\right) \cdots \left(1-\frac{1}{p_n}\right) </math>. |
=== Identities === | === Identities === | ||
Revision as of 11:55, 20 June 2006
Euler's totient function, 
, is defined as the number of positive integers less than or equal to a given positive integer that are relatively prime to that integer.
Formulas
The formal definition is 
.
Given the prime factorization of 
, one can compute using the formula 
.
Identities
For prime p, 
, because all numbers less than 
are relatively prime to it.
For relatively prime 
, 
.
In fact, we also have for any that 
.
For any 
, we have 
where the sum is taken over all divisors d of .
