diff --git a/rust/Cargo.lock b/rust/Cargo.lock
index aa1924c..8dee346 100644
--- a/rust/Cargo.lock
+++ b/rust/Cargo.lock
@@ -1,4 +1,25 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "either"
+version = "1.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "euler-rust"
 version = "0.1.0"
+dependencies = [
+ "itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
 
+[[package]]
+name = "itertools"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "either 1.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[metadata]
+"checksum either 1.5.3 (registry+https://github.com/rust-lang/crates.io-index)" = "bb1f6b1ce1c140482ea30ddd3335fc0024ac7ee112895426e0a629a6c20adfe3"
+"checksum itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5b8467d9c1cebe26feb08c640139247fac215782d35371ade9a2136ed6085358"
diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 014ac82..b283821 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -4,3 +4,4 @@ version = "0.1.0"
 authors = ["evan hemsley <evan.hemsley@gmail.com>"]
 
 [dependencies]
+itertools = "0.8"
\ No newline at end of file
diff --git a/rust/src/euler/mod.rs b/rust/src/euler/mod.rs
index 43bdc02..1dd8e64 100644
--- a/rust/src/euler/mod.rs
+++ b/rust/src/euler/mod.rs
@@ -2,4 +2,5 @@ pub mod prime;
 
 pub mod problem_001;
 pub mod problem_002;
-pub mod problem_003;
\ No newline at end of file
+pub mod problem_003;
+pub mod problem_004;
\ No newline at end of file
diff --git a/rust/src/euler/prime.rs b/rust/src/euler/prime.rs
index b2aeabc..c5f41a2 100644
--- a/rust/src/euler/prime.rs
+++ b/rust/src/euler/prime.rs
@@ -11,7 +11,7 @@ fn subfactors(mut n: u64, p: u64) -> (u64, Vec<u64>) {
         r = n % p;
     }
 
-    return (n, subfactors);
+    (n, subfactors)
 }
 
 pub fn trial_factorization(mut n: u64) -> Vec<u64> {
@@ -39,7 +39,7 @@ pub fn trial_factorization(mut n: u64) -> Vec<u64> {
         p += 4;
     }
     if n >= 1 { factors.push(n); }
-    return factors;
+    factors
 }
 
 #[cfg(test)]
diff --git a/rust/src/euler/problem_001.rs b/rust/src/euler/problem_001.rs
index 127fe03..0b77170 100644
--- a/rust/src/euler/problem_001.rs
+++ b/rust/src/euler/problem_001.rs
@@ -1,5 +1,5 @@
-fn solution() -> i32 {
-    return (1..1000).filter( |n| (n % 3 == 0) || (n % 5 == 0)).sum();
+pub fn solution() -> i32 {
+    (1..1000).filter( |n| (n % 3 == 0) || (n % 5 == 0)).sum()
 }
 
 #[cfg(test)]
@@ -8,6 +8,6 @@ mod tests {
 
     #[test]
     fn problem_001() {
-        assert_eq!(solution(), 233168);
+        assert_eq!(solution(), 233_168);
     }
 }
diff --git a/rust/src/euler/problem_002.rs b/rust/src/euler/problem_002.rs
index 9e65ef2..5e12d53 100644
--- a/rust/src/euler/problem_002.rs
+++ b/rust/src/euler/problem_002.rs
@@ -21,11 +21,11 @@ fn fibonacci() -> Fibonacci {
 }
 
 fn fibonacci_sum_up_to(number: u32) -> u32 {
-    return fibonacci().take_while(|n| n < &number).filter(|n| n % 2 == 0).sum();
+    fibonacci().take_while(|n| *n < number).filter(|n| n % 2 == 0).sum()
 }
 
-fn solution() -> u32 {
-    return fibonacci_sum_up_to(4000000);
+pub fn solution() -> u32 {
+    fibonacci_sum_up_to(4_000_000)
 }
 
 #[cfg(test)]
@@ -34,6 +34,6 @@ mod tests {
 
     #[test]
     fn problem_002() {
-        assert_eq!(solution(), 4613732);
+        assert_eq!(solution(), 4_613_732);
     }
 }
\ No newline at end of file
diff --git a/rust/src/euler/problem_003.rs b/rust/src/euler/problem_003.rs
index e259782..7a793a9 100644
--- a/rust/src/euler/problem_003.rs
+++ b/rust/src/euler/problem_003.rs
@@ -1,7 +1,7 @@
 use euler::prime;
 
-fn solution() -> Option<u64> {
-    return prime::trial_factorization(600851475143).last().cloned();
+pub fn solution() -> Option<u64> {
+    prime::trial_factorization(600_851_475_143).last().cloned()
 }
 
 #[cfg(test)]
diff --git a/rust/src/euler/problem_004.rs b/rust/src/euler/problem_004.rs
new file mode 100644
index 0000000..66cfc46
--- /dev/null
+++ b/rust/src/euler/problem_004.rs
@@ -0,0 +1,22 @@
+use itertools::Itertools;
+
+fn palindrome(n: u64) -> bool {
+    let num_string = n.to_string();
+    let half = num_string.len() / 2;
+
+    num_string.bytes().take(half).eq(num_string.bytes().rev().take(half))
+}
+
+pub fn solution() -> Option<u64> {
+    (100..1000).tuple_combinations().map( |(a, b)| a * b ).filter( |n| palindrome(*n)).max()
+}
+
+#[cfg(test)]
+mod tests {
+    use euler::problem_004::solution;
+
+    #[test]
+    fn problem_004() {
+        assert_eq!(solution(), Some(906_609));
+    }
+}
\ No newline at end of file
diff --git a/rust/src/lib.rs b/rust/src/lib.rs
index f20075a..d28fbf9 100644
--- a/rust/src/lib.rs
+++ b/rust/src/lib.rs
@@ -1 +1,3 @@
+extern crate itertools;
+
 pub mod euler;