From 3ac82ee526a44b7d95f5c4e43c4c2d93b56dc553 Mon Sep 17 00:00:00 2001
From: Stefan Harmuth <pennywise@drock.de>
Date: Thu, 10 Oct 2024 15:33:39 +0200
Subject: [PATCH] int_seq.hexagonal()

---
 src/tools/int_seq.py | 7 +++++++
 1 file changed, 7 insertions(+)

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)