#### Compute Totient

```// Totient function for
// all numbers smaller than
// or equal to n.

// Computes and prints
// totient of all numbers
// smaller than or equal to n

use std::vec;

pub fn compute_totient(n: i32) -> vec::Vec<i32> {
let mut phi: Vec<i32> = Vec::new();

// initialize phi[i] = i
for i in 0..=n {
phi.push(i);
}

// Compute other Phi values
for p in 2..n + 1 {
// If phi[p] is not computed already,
// then number p is prime
if phi[(p) as usize] == p {
// Phi of a prime number p is
// always equal to p-1.
phi[(p) as usize] = p - 1;

// Update phi values of all
// multiples of p
for i in ((2 * p)..n + 1).step_by(p as usize) {
phi[(i) as usize] = (phi[i as usize] / p) * (p - 1);
}
}
}

phi[1..].to_vec()
}

#[cfg(test)]
mod tests {
use super::*;

#[test]
fn test_1() {
assert_eq!(
compute_totient(12),
vec![1, 1, 2, 2, 4, 2, 6, 4, 6, 4, 10, 4]
);
}

#[test]
fn test_2() {
assert_eq!(compute_totient(7), vec![1, 1, 2, 2, 4, 2, 6]);
}

#[test]
fn test_3() {
assert_eq!(compute_totient(4), vec![1, 1, 2, 2]);
}
}
```