diff --git a/src/tools/int_seq.py b/src/tools/int_seq.py
index 810a943..8db57da 100644
--- a/src/tools/int_seq.py
+++ b/src/tools/int_seq.py
@@ -38,3 +38,10 @@ def pentagonal(n: int) -> int:
     0, 1, 5, 12, 22, 35, ...
     """
     return ((3 * n * n) - n) // 2
+
+
+def hexagonal(n: int) -> int:
+    if n == 1:
+        return 1
+
+    return n * 2 + (n - 1) * 2 + (n - 2) * 2 + hexagonal(n - 1)