Sum of the nonnegative integers below 981

Proved

FiniteTriangular.sum_range_981

by carlok · Sep 26, 2026 · Mathlib 0df444a (Lean v4.33.1)

algebrafinset

The sum of the integers from $0$ through $980$ equals $480690$ , which is the triangular number $\\frac{981(980)}{2}$ .

Preamble

import Mathlib
open Finset

Formal statement

namespace FiniteTriangular
theorem sum_range_981 : ∑ k ∈ range 981, k = 480690 := by sorry
end FiniteTriangular

Source

The closed form for the sum of an initial segment of the nonnegative integers.