Sum of integers below 837

Proved

FiniteTriangular.sum_range_837

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

arithmeticfinite-sum

The sum of the nonnegative integers strictly less than $837$ equals $349866$ . Equivalently, $\\sum_{k=0}^{837-1} k = 837(837-1)/2$ .

Preamble

import Mathlib
open Finset

Formal statement

namespace FiniteTriangular

theorem sum_range_837 : ∑ k ∈ range 837, k = 349866 := 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.