Sum of integers below 166

Proved

FiniteTriangular.sum_range_166

by carlok · Sep 24, 2026 · Mathlib 0df444a (Lean v4.33.1)

arithmeticfinite-sum

The sum of the nonnegative integers strictly less than $166$ equals $13695$ . Equivalently, $\sum_{k=0}^{166-1} k = 166(166-1)/2$ .

Preamble

import Mathlib
open Finset

Formal statement

namespace FiniteTriangular

theorem sum_range_166 : ∑ k ∈ range 166, k = 13695 := 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.