diff --git a/src/bin/problem_21.rs b/src/bin/problem_21.rs
index 782015c..5a7282b 100644
--- a/src/bin/problem_21.rs
+++ b/src/bin/problem_21.rs
@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 use std::time::Instant;
 
 fn main() {
@@ -6,40 +6,38 @@ fn main() {
     let mut amicable_cache: HashMap<isize, isize> = HashMap::new();
     let mut despicable_cache: HashMap<isize, isize> = HashMap::new();
     let mut sum_amicable = 0;
-    for i in 2..=10 {
-        if amicable_cache.get(&i).is_some() {
-            continue;
-        }
-        if despicable_cache.get(&i).is_some() {
-            continue;
-        }
+    for i in 2..10000 {
         let divisors = get_divisors(i);
         let sum_divisors = divisors.iter().sum();
+        if amicable_cache.get(&sum_divisors).is_some() {
+            continue;
+        }
+        if despicable_cache.get(&sum_divisors).is_some() {
+            continue;
+        }
         let other_divisors = get_divisors(sum_divisors);
         let other_sum_divisors = other_divisors.iter().sum();
-        if sum_divisors == other_sum_divisors {
-            println!("{:?}", divisors);
+        if i == other_sum_divisors && i != sum_divisors {
             amicable_cache.insert(other_sum_divisors, sum_divisors);
             sum_amicable += sum_divisors + other_sum_divisors;
         } else {
-            println!("{:?}", divisors);
             despicable_cache.insert(other_sum_divisors, sum_divisors);
         }
     }
-    println!("{:?}", amicable_cache);
-    println!("{sum_amicable}");
+    println!("cache: {:?}", amicable_cache);
+    println!("sum: {sum_amicable}");
     println!("Time={} µs", now.elapsed().as_micros());
 }
 
 fn get_divisors(n: isize) -> Vec<isize> {
-    let mut divisors = vec![1];
+    let mut divisors = HashSet::from([1]);
     let mut potential_divisor = 2;
-    while (potential_divisor * potential_divisor) < n {
+    while (potential_divisor * potential_divisor) <= n {
         if n % potential_divisor == 0 {
-            divisors.push(potential_divisor);
-            divisors.push(n / potential_divisor);
+            divisors.insert(potential_divisor);
+            divisors.insert(n / potential_divisor);
         }
         potential_divisor = potential_divisor + 1;
     }
-    divisors
+    divisors.iter().map(|&divisor| divisor).collect()
 }
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