diff --git a/lib/primes/src/lib.rs b/lib/primes/src/lib.rs
index 9b8af4a..a1c406d 100644
--- a/lib/primes/src/lib.rs
+++ b/lib/primes/src/lib.rs
@@ -1,10 +1,14 @@
 extern crate num;
 
+use std::collections::HashSet;
+use std::fmt::Display;
+use std::fs::File;
+use std::hash::Hash;
+use std::io::Write;
+
 use num::FromPrimitive;
 use num::Num;
 use num::ToPrimitive;
-use std::collections::HashSet;
-use std::hash::Hash;
 
 #[derive(Clone)]
 pub struct Primes<T> {
@@ -14,7 +18,7 @@ pub struct Primes<T> {
 
 impl<T> Primes<T>
 where
-    T: Num + ToPrimitive + FromPrimitive + Hash + Eq + PartialEq + Copy,
+    T: Num + ToPrimitive + FromPrimitive + Hash + Eq + PartialEq + Copy + Display,
 {
     pub fn get_between(min_value: T, max_value: T) -> Self {
         let max_value = max_value.to_usize().unwrap();
@@ -47,19 +51,13 @@ where
         let length = *max_value - *min_value;
         let mut result = vec![true; length];
 
-        for number_to_check in 2..(max_value / 2) {
-            let mut last_number = number_to_check;
-            loop {
-                let current_number = last_number + number_to_check;
-                if current_number < *min_value {
-                    last_number = current_number;
+        let upper_limit = f64::sqrt(*max_value as f64).ceil() as usize;
+        for i in 2..upper_limit {
+            for multiple in ((i * i)..*max_value).step_by(i) {
+                if &multiple < min_value {
                     continue;
                 }
-                if current_number >= *max_value {
-                    break;
-                }
-                result[current_number - min_value] = false;
-                last_number = current_number;
+                result[multiple - min_value] = false;
             }
         }
         result
@@ -72,10 +70,10 @@ where
         };
     }
 
-    // pub fn len(&self) -> usize {
-    //     debug_assert_eq!(self.vector.len(), self.set.len());
-    //     self.vector.len()
-    // }
+    pub fn len(&self) -> usize {
+        debug_assert_eq!(self.vector.len(), self.set.len());
+        self.vector.len()
+    }
 
     pub fn pop(&mut self) -> Option<T> {
         let result = self.vector.pop();
@@ -88,11 +86,18 @@ where
     pub fn contains(&self, val: &T) -> bool {
         self.set.contains(val)
     }
+
+    pub fn save(&self, filename: &str) {
+        let mut f = File::create(filename).unwrap();
+        for p in &self.vector {
+            writeln!(f, "{p}").unwrap();
+        }
+    }
 }
 
 #[cfg(test)]
 mod test {
-    use crate::primes::Primes;
+    use super::Primes;
 
     #[test]
     fn test_example_prime() {
@@ -113,8 +118,25 @@ mod test {
     #[test]
     fn test_pop() {
         let mut primes = Primes::get_between(10, 20);
-        assert!(primes.contains(&11));
+        assert_eq!(primes.len(), 4);
+        assert!(primes.contains(&19));
+
         primes.pop();
+
+        assert_eq!(primes.len(), 3);
         assert!(!primes.contains(&11));
     }
+
+    #[test]
+    fn test_example_2() {
+        let primes = Primes::get_between(2, 100_000);
+        assert_eq!(primes.len(), 9_592);
+    }
+
+    #[ignore]
+    #[test]
+    fn test_performance() {
+        let primes = Primes::get_between(2, 10_000_000);
+        assert_eq!(primes.len(), 664_579);
+    }
 }