diff --git a/README.rst b/README.rst
index b2f1ec28..af4c1b47 100644
--- a/README.rst
+++ b/README.rst
@@ -69,7 +69,7 @@ Olivia's Project Euler Solutions
    |            | C11+ in: |msvc| [1]_       |        | |CodeQL| |br|     |
    |            | |br| Browser [2]_          |        | |C-lint|          |
    +------------+----------------------------+--------+-------------------+
-   | C++        | C++98+ in: |br| |clang|, & | 19     | |Cpi| |br|        |
+   | C++        | C++98+ in: |br| |clang|, & | 20     | |Cpi| |br|        |
    |            | |gcc| |br|                 |        | |Cp-Cov| |br|     |
    |            | C++14+ in: |msvc| [1]_     |        | |CodeQL| |br|     |
    |            | |br| Browser [3]_          |        | |Cp-lint|         |
diff --git a/cplusplus/README.rst b/cplusplus/README.rst
index 7776f70d..e8df89d8 100644
--- a/cplusplus/README.rst
+++ b/cplusplus/README.rst
@@ -167,6 +167,7 @@ Problems Solved
 
 -  ☒ `1 <./src/p0001.cpp>`__
 -  ☒ `2 <./src/p0002.cpp>`__
+-  ☒ `3 <./src/p0003.cpp>`__
 -  ☒ `4 <./src/p0004.cpp>`__
 -  ☒ `6 <./src/p0006.cpp>`__
 -  ☒ `7 <./src/p0007.cpp>`__
diff --git a/cplusplus/src/include/primes.hpp b/cplusplus/src/include/primes.hpp
index 30108f97..bb5bb0a2 100644
--- a/cplusplus/src/include/primes.hpp
+++ b/cplusplus/src/include/primes.hpp
@@ -4,6 +4,7 @@
 #include <vector>
 #include <map>
 #include <limits>
+#include <stdexcept>
 
 template<typename T>
 class PrimeGenerator {
@@ -17,7 +18,7 @@ class PrimeGenerator {
     T next() {
         if (has_limit && prime >= limit) {
             sieve.clear();
-            return T(-1);
+            throw new std::runtime_error("Tried to exceed given limit (or limit of data type).");
         }
         prime = next_prime(candidate);
         candidate = prime + T(1);
@@ -71,3 +72,40 @@ template<typename T>
 PrimeGenerator<T> primes_until(T x) {
     return PrimeGenerator<T>(x);
 }
+
+template<typename T>
+class PrimeFactors {
+public:
+    PrimeFactors(T target) 
+        : target(target), last_prime(T(std::numeric_limits<T>::max())), prime_gen(primes<T>()) {}
+
+    T next() {
+        if (!has_next())
+            throw new std::runtime_error("No more factors available.");
+        if (std::numeric_limits<T>::min() < 0 && target < 0) {
+            target = -target;
+            return T(-1);
+        }
+        while (true) {
+            if (target % last_prime == 0) {
+                target /= last_prime;
+                return last_prime;
+            }
+            last_prime = prime_gen.next();
+        }
+    }
+
+    bool has_next() const {
+        return target != 1 && target != 0;
+    }
+
+private:
+    T target;
+    T last_prime;
+    PrimeGenerator<T> prime_gen;
+};
+
+template<typename T>
+PrimeFactors<T> prime_factors(T target) {
+    return PrimeFactors<T>(target);
+}
diff --git a/cplusplus/src/p0003.cpp b/cplusplus/src/p0003.cpp
new file mode 100644
index 00000000..457dc53f
--- /dev/null
+++ b/cplusplus/src/p0003.cpp
@@ -0,0 +1,30 @@
+/*
+Project Euler Problem 3
+
+More lazy functions this time.
+
+Problem:
+
+The prime factors of 13195 are 5, 7, 13 and 29.
+
+What is the largest prime factor of the number 600851475143 ?
+*/
+
+#ifndef EULER_P0003
+#define EULER_P0003
+#include <stdint.h>
+#include <iostream>
+#include "include/macros.hpp"
+#include "include/primes.hpp"
+
+uint16_t EMSCRIPTEN_KEEPALIVE p0003() {
+    uint16_t answer = 0;
+    PrimeFactors<uint64_t> pfs = prime_factors<uint64_t>(600851475143);
+    while (pfs.has_next())
+        answer = (uint16_t) pfs.next();
+    return answer;
+}
+
+
+PROGRAM_TAIL(p0003)
+#endif
diff --git a/cplusplus/test.cpp b/cplusplus/test.cpp
index cf83aed5..9d176bd8 100644
--- a/cplusplus/test.cpp
+++ b/cplusplus/test.cpp
@@ -5,7 +5,7 @@
 #include <inttypes.h>
 #include "src/p0001.cpp"
 #include "src/p0002.cpp"
-// #include "src/p0003.cpp"
+#include "src/p0003.cpp"
 #include "src/p0004.cpp"
 // #include "src/p0005.cpp"
 #include "src/p0006.cpp"
@@ -37,7 +37,7 @@ typedef struct {
 ProblemRef answers[] = {
 	{   1,	(void *(*)())p0001 },
 	{   2, 	(void *(*)())p0002 },
-	// {   3,	(void *(*)())p0003 },
+	{   3,	(void *(*)())p0003 },
 	{   4,	(void *(*)())p0004 },
 	// {   5,	(void *(*)())p0005 },
 	{   6,	(void *(*)())p0006 },
diff --git a/cplusplus/test_euler.py b/cplusplus/test_euler.py
index 9880db9e..bb82c982 100644
--- a/cplusplus/test_euler.py
+++ b/cplusplus/test_euler.py
@@ -22,9 +22,7 @@
 
 answers = {
     x: get_answer(x) for x in (
-        1,
-        2,
-        4,
+        *range(1, 5),
         *range(6, 10),
         11,
         *range(13, 18),
diff --git a/docs/index.rst b/docs/index.rst
index 4ca13236..a5a0a6e7 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -80,7 +80,7 @@ Problems Solved
   +-----------+------------+------------+------------+------------+------------+------------+------------+
   |:prob:`002`|:c-d:`0002` |:cp-d:`0002`|:cs-d:`0002`|:ja-d:`0002`|:js-d:`0002`|:py-d:`0002`|:rs-d:`0002`|
   +-----------+------------+------------+------------+------------+------------+------------+------------+
-  |:prob:`003`|:c-d:`0003` |            |:cs-d:`0003`|            |:js-d:`0003`|:py-d:`0003`|:rs-d:`0003`|
+  |:prob:`003`|:c-d:`0003` |:cp-d:`0003`|:cs-d:`0003`|            |:js-d:`0003`|:py-d:`0003`|:rs-d:`0003`|
   +-----------+------------+------------+------------+------------+------------+------------+------------+
   |:prob:`004`|:c-d:`0004` |:cp-d:`0004`|:cs-d:`0004`|:ja-d:`0004`|:js-d:`0004`|:py-d:`0004`|:rs-d:`0004`|
   +-----------+------------+------------+------------+------------+------------+------------+------------+
diff --git a/docs/src/cplusplus/lib/primes.rst b/docs/src/cplusplus/lib/primes.rst
index 70624e01..887b3a54 100644
--- a/docs/src/cplusplus/lib/primes.rst
+++ b/docs/src/cplusplus/lib/primes.rst
@@ -10,9 +10,10 @@ Includes
 - :external:cpp:type:`vector`
 - :external:cpp:type:`map`
 - :external:cpp:type:`limits`
+- :external:cpp:type:`stdexcept`
 
 .. cpp:namespace-push:: primes
-    
+
 .. cpp:class:: PrimeGenerator
 
   .. cpp:function:: PrimeGenerator<T> PrimeGenerator<T>()
@@ -26,9 +27,24 @@ Includes
 
     These constructors will return a finite generator of prime numbers, going to ``upper_limit``.
 
-  .. cpp:function:: bool next()
+  .. cpp:function:: T next()
+
+    Returns the next prime, or ``0`` if it is above the defined limit.
+
+  .. cpp:function:: bool has_next()
+
+    Returns ``true`` if there is a next value to generate.
+    
+.. cpp:class:: PrimeFactors
+
+  .. cpp:function:: PrimeFactors<T> PrimeFactors<T>(T upper_limit)
+  .. cpp:function:: PrimeFactors<T> prime_factors<T>(T upper_limit)
+
+    These constructors will return a finite generator of prime factors of ``target``.
+
+  .. cpp:function:: T next()
 
-    Returns the next prime, or ``-1`` if it is above the defined limit.
+    Returns the next prime factor, or ``0`` if it is above the defined limit.
 
   .. cpp:function:: bool has_next()
 
diff --git a/docs/src/cplusplus/p0003.rst b/docs/src/cplusplus/p0003.rst
new file mode 100644
index 00000000..2b51ab56
--- /dev/null
+++ b/docs/src/cplusplus/p0003.rst
@@ -0,0 +1,30 @@
+C++ Implementation of Problem 3
+===============================
+
+View source code :source:`cplusplus/src/p0003.cpp`
+
+Includes
+--------
+
+- `"primes.hpp" <./lib/primes.html>`__
+- :external:c:type:`stdint`
+- :external:cpp:type:`iostream`
+
+Solution
+--------
+
+.. cpp:namespace-push:: p0003
+
+.. cpp:function:: uint16_t p0003()
+
+.. cpp:function:: int main(int argc, char const *argv[])
+
+   .. note:: 
+      
+      This function is only present in the Python test runner, or when compiling as a standalone program.
+
+.. literalinclude:: ../../../cplusplus/src/p0003.cpp
+   :language: C++
+   :linenos:
+
+.. tags:: fibonacci-number, divisibility