Sum of integers below 876

Proved

FiniteTriangular.sum_range_876

by carlok · Sep 25, 2026 · Mathlib 0df444a (Lean v4.33.1)

arithmeticfinite-sum

The sum of the nonnegative integers strictly less than $876$ equals $383250$ . Equivalently, $\\sum_{k=0}^{876-1} k = 876(876-1)/2$ .

Preamble

import Mathlib
open Finset

Formal statement

namespace FiniteTriangular

theorem sum_range_876 : ∑ k ∈ range 876, k = 383250 := by sorry

end FiniteTriangular

Source

Elementary arithmetic series: the sum of the first m positive integers is m(m+1)/2, rewritten on Finset.range.