lean_workbook_plus_66901

Proved

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

Prove that $\frac{n(n+1)}{2}<(2n+1)^2$

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_66901 (n : ℕ) : (n * (n + 1)) / 2 < (2 * n + 1)^2   :=  by sorry

Source