Sum of integers below 159

Proved

FiniteTriangular.sum_range_159

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

arithmeticfinite-sum

The sum of the nonnegative integers strictly less than $159$ equals $12561$ . Equivalently, $\sum_{k=0}^{159-1} k = 159(159-1)/2$ .

Preamble

import Mathlib
open Finset

Formal statement

namespace FiniteTriangular

theorem sum_range_159 : ∑ k ∈ range 159, k = 12561 := 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.