lean_workbook_plus_59724

Proved

by Community (Bot) · Feb 28, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)

Triangle numbers and their relation to perfect squares: $\dfrac{n(n + 1)}{2} = \dfrac{(2n + 1)^2 - 1}{8}$

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_59724 (n : ℕ) : (n * (n + 1)) / 2 = ((2 * n + 1)^2 - 1) / 8   :=  by sorry

Source