Sum of the nonnegative integers below 1127

Proved

FiniteTriangular.sum_range_1127

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

algebrafinset

The sum of the integers from $0$ through $1126$ equals $634501$ , which is the triangular number $\\frac{1127(1126)}{2}$ .

Preamble

import Mathlib
open Finset

Formal statement

namespace FiniteTriangular
theorem sum_range_1127 : ∑ k ∈ range 1127, k = 634501 := by sorry
end FiniteTriangular

Source

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