diff --git a/reasoning_gym/algorithmic/__init__.py b/reasoning_gym/algorithmic/__init__.py
index ad76199f..dd3c6758 100644
--- a/reasoning_gym/algorithmic/__init__.py
+++ b/reasoning_gym/algorithmic/__init__.py
@@ -25,6 +25,7 @@ from .spiral_matrix import SpiralMatrixConfig, SpiralMatrixDataset
 from .word_ladder import WordLadderConfig, WordLadderDataset
 from .word_sequence_reversal import WordSequenceReversalConfig, WordSequenceReversalDataset
 from .word_sorting import TextTransformation, WordSortingConfig, WordSortingDataset
+from .count_primes import CountPrimesConfig, CountPrimesDataset
 
 __all__ = [
     "SpellBackwardConfig",
@@ -66,4 +67,6 @@ __all__ = [
     "ManipulateMatrixDataset",
     "BinaryMatrixConfig",
     "BinaryMatrixDataset",
+    "CountPrimesConfig",
+    "CountPrimesDataset",
 ]
diff --git a/reasoning_gym/algorithmic/count_primes.py b/reasoning_gym/algorithmic/count_primes.py
new file mode 100644
index 00000000..3335371c
--- /dev/null
+++ b/reasoning_gym/algorithmic/count_primes.py
@@ -0,0 +1,60 @@
+"""Count prime numbers in a given interval.
+
+Solution obtained with Sieve of Eratosthenes:
+https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
+"""
+
+import math
+from dataclasses import dataclass
+from random import Random
+from typing import Optional
+
+from ..factory import ProceduralDataset, register_dataset
+
+QUESTION_TEMPLATE = """Count how many prime numbers there are between {start} and {end} (inclusive) ?"""
+
+@dataclass
+class CountPrimesConfig:
+    """Configuration for Count Primes dataset generation"""
+
+    max_n: int = 10_000  # Upper bound for the interval
+
+    size: int = 500  # Virtual dataset size
+    seed: Optional[int] = None
+
+    def validate(self):
+        """Validate configuration parameters"""
+        assert 1 <= self.max_n, "max_n must be at least 1"
+
+class CountPrimesDataset(ProceduralDataset):
+    """Generates Count Primes exercises with configurable difficulty"""
+
+    def __init__(self, config: CountPrimesConfig):
+        super().__init__(config=config, seed=config.seed, size=config.size)
+        self.primes = self._get_primes(config.max_n + 1)
+    
+    def _get_primes(self, n: int) -> list[bool]:
+        if n <= 1:
+            return []
+        primes = [True] * n
+        primes[0] = primes[1] = False
+        for i in range(2, int(math.sqrt(n))+1):
+            if primes[i]:
+                for j in range(2*i, n, i):
+                    primes[j] = False
+        return primes
+
+    def __getitem__(self, idx: int) -> dict:
+        """Generate a single Count Primes question"""
+        rng = Random(self.seed + idx)
+        start = rng.randint(1, self.config.max_n)
+        end = rng.randint(start, self.config.max_n)
+        primes = self.primes[start:end+1]
+        answer = sum(primes)
+        return {
+            "question": QUESTION_TEMPLATE.format(start=start, end=end),
+            "answer": str(answer),
+            "metadata": {"start": start, "end": end, "primes": primes, "solution": answer},
+        }
+
+register_dataset("count_primes", CountPrimesDataset, CountPrimesConfig)
diff --git a/tests/test_count_primes.py b/tests/test_count_primes.py
new file mode 100644
index 00000000..d88981e9
--- /dev/null
+++ b/tests/test_count_primes.py
@@ -0,0 +1,89 @@
+"""Tests for Count Primes questions generation"""
+
+import pytest
+
+from reasoning_gym.algorithmic.count_primes import CountPrimesConfig, CountPrimesDataset
+
+
+def test_count_primes_config_validation():
+    """Test that invalid configs raise appropriate errors"""
+    with pytest.raises(AssertionError):
+        config = CountPrimesConfig(max_n=-1)  # Negative not allowed
+        config.validate()
+
+    with pytest.raises(AssertionError):
+        config = CountPrimesConfig(max_n=0)  # Zero not allowed
+        config.validate()
+
+
+
+def test_count_primes_dataset_deterministic():
+    """Test that dataset generates same items with same seed"""
+    config = CountPrimesConfig(seed=42, size=10)
+    dataset1 = CountPrimesDataset(config)
+    dataset2 = CountPrimesDataset(config)
+
+    for i in range(len(dataset1)):
+        assert dataset1[i] == dataset2[i]
+
+
+def test_count_primes_dataset_items():
+    """Test basic properties of generated items"""
+    config = CountPrimesConfig(max_n=10, size=10, seed=42)
+    dataset = CountPrimesDataset(config)
+
+    for i in range(len(dataset)):
+        item = dataset[i]
+        # Check item structure
+        assert isinstance(item, dict)
+        assert "question" in item
+        assert "answer" in item
+        assert "metadata" in item
+
+        # Check metadata
+        assert "start" in item["metadata"]
+        assert "end" in item["metadata"]
+        assert "primes" in item["metadata"]
+        assert "solution" in item["metadata"]
+
+        start = item["metadata"]["start"]
+        end = item["metadata"]["end"]
+        primes = item["metadata"]["primes"]
+
+        assert start <= end
+        assert len(primes) <= end - start + 1
+
+
+def test_count_primes_dataset_iteration():
+    """Test that iteration respects dataset size"""
+    config = CountPrimesConfig(size=5, seed=42)
+    dataset = CountPrimesDataset(config)
+
+    items = list(dataset)
+    assert len(items) == config.size
+
+    # Test multiple iterations yield same items
+    assert items == list(dataset)
+
+
+def test_count_primes_answer():
+    """Test the _get_primes method"""
+    config = CountPrimesConfig(seed=42)
+    dataset = CountPrimesDataset(config)
+
+    # Base cases
+    assert dataset._get_primes(n=0) == []
+    assert dataset._get_primes(n=1) == []
+    assert dataset._get_primes(n=2) == [False, False]
+
+    # Test primes up to 10
+    primes = dataset._get_primes(n=11)
+    assert primes[2] == True
+    assert primes[3] == True
+    assert primes[4] == False
+    assert primes[5] == True
+    assert primes[6] == False
+    assert primes[7] == True
+    assert primes[8] == False
+    assert primes[9] == False
+    assert primes[10] == False
\ No newline at end of file