--- /dev/null
+++ b/Mathlib/Unsorry/SumRangeSqClosedForm.lean
@@ -0,0 +1,14 @@
+/-
+Copyright (c) 2026 Chris Barlow. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Chris Barlow
+-/
+import Mathlib.Algebra.BigOperators.Group.Finset.Basic
+import Mathlib.Tactic.Ring
+
+theorem sum_range_sq_closed_form (n : ℕ) : 6 * ∑ i ∈ Finset.range (n + 1), i ^ 2 = n * (n + 1) * (2 * n + 1) := by
+  induction n with
+  | zero => simp
+  | succ k ih =>
+    rw [Finset.sum_range_succ, mul_add, ih]
+    ring