Sum of integers below 363

Proved

FiniteTriangular.sum_range_363

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

arithmeticfinite-sum

The sum of the nonnegative integers strictly less than $363$ equals $65703$ . Equivalently, $\\sum_{k=0}^{363-1} k = 363(363-1)/2$ .

Preamble

import Mathlib
open Finset

Formal statement

namespace FiniteTriangular

theorem sum_range_363 : ∑ k ∈ range 363, k = 65703 := 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.