Sum of the nonnegative integers below 1131
ProvedFiniteTriangular.sum_range_1131algebrafinset
The sum of the integers from through equals , which is the triangular number .
Preamble
import Mathlib open Finset
Formal statement
namespace FiniteTriangular theorem sum_range_1131 : ∑ k ∈ range 1131, k = 639015 := by sorry end FiniteTriangular
Source
The closed form for the sum of an initial segment of the nonnegative integers.