diff --git a/src/euler27/Cargo.toml b/src/euler27/Cargo.toml
index 2b3f298..9930c4a 100644
--- a/src/euler27/Cargo.toml
+++ b/src/euler27/Cargo.toml
@@ -4,3 +4,10 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
+
+[dev-dependencies]
+rstest = "0.25.0"
+
+[profile.release]
+debug = true
+lto = "fat"
diff --git a/src/euler27/src/main.rs b/src/euler27/src/main.rs
index 6cfd4b1..30abf8d 100644
--- a/src/euler27/src/main.rs
+++ b/src/euler27/src/main.rs
@@ -1,15 +1,27 @@
 use std::collections::HashMap;
 
 fn main() {
-    let q = Quadratic { a: 1, b: 41 };
+    let mut primes = Primes::new();
 
-    let mut p = Primes::new();
+    let mut maximum_number_primes = 0;
+    let mut maximum_product = 0;
 
-    for n in 0..=39 {
-        let result = q.calculate(n);
-        dbg!(p.is_prime(n));
-        println!("{}", result);
+    for a in -999..=999 {
+        for b in -1000..=1000 {
+            let quadratic = Quadratic::new(a, b);
+
+            'inner: for number_consecutive_primes in 0.. {
+                if !primes.is_prime(quadratic.calculate(number_consecutive_primes)) {
+                    if number_consecutive_primes > maximum_number_primes {
+                        maximum_number_primes = number_consecutive_primes;
+                        maximum_product = quadratic.product();
+                    }
+                    break 'inner;
+                }
+            }
+        }
     }
+    println!("{maximum_product}");
 }
 
 struct Quadratic {
@@ -18,9 +30,17 @@ struct Quadratic {
 }
 
 impl Quadratic {
+    fn new(a: isize, b: isize) -> Self {
+        Self { a, b }
+    }
+
     fn calculate(&self, n: isize) -> isize {
         n.pow(2) + self.a * n + self.b
     }
+
+    fn product(&self) -> isize {
+        self.a * self.b
+    }
 }
 
 struct Primes(HashMap<isize, bool>);
@@ -32,6 +52,9 @@ impl Primes {
     }
 
     fn is_prime(&mut self, number: isize) -> bool {
+        if number < 2 {
+            return false;
+        }
         let value = self.0.get(&number);
         if let Some(result) = value {
             return *result;
@@ -42,6 +65,67 @@ impl Primes {
     }
 
     fn test_primality(number: isize) -> bool {
-        let max = (number as f64).sqrt();
+        let max = (number as f64).sqrt().floor() as isize;
+        for divisor in 2..=max {
+            if number % divisor == 0 {
+                return false;
+            }
+        }
+        true
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{Primes, Quadratic};
+
+    use rstest::rstest;
+
+    #[rstest]
+    #[case(2, true)]
+    #[case(3, true)]
+    #[case(7, true)]
+    #[case(9, false)]
+    #[case(27, false)]
+    fn test_basic_primes(#[case] number: isize, #[case] expected: bool) {
+        let mut primes = Primes::new();
+        let result = primes.is_prime(number);
+        assert_eq!(result, expected)
+    }
+
+    #[test]
+    fn test_eulers_equation() {
+        let q = Quadratic::new(1, 41);
+        let mut primes = Primes::new();
+        for n in 0..=39 {
+            let possible_prime = q.calculate(n);
+            let result = primes.is_prime(possible_prime);
+            assert!(result);
+        }
+
+        let possible_prime = q.calculate(40);
+        let result = primes.is_prime(possible_prime);
+        assert!(!result);
+    }
+
+    #[test]
+    fn test_second_equation() {
+        let q = Quadratic::new(-79, 1601);
+        let mut primes = Primes::new();
+        for n in 0..=79 {
+            let possible_prime = q.calculate(n);
+            let result = primes.is_prime(possible_prime);
+            assert!(result);
+        }
+
+        let possible_prime = q.calculate(80);
+        let result = primes.is_prime(possible_prime);
+        assert!(!result);
+    }
+
+    #[test]
+    fn product() {
+        let product = Quadratic::new(-79, 1601).product();
+        assert_eq!(product, -126479)
     }
 }