Sum of the nonnegative integers below 1123
ProvedFiniteTriangular.sum_range_1123algebrafinset
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_1123 : ∑ k ∈ range 1123, k = 630003 := by sorry end FiniteTriangular
Source
The closed form for the sum of an initial segment of the nonnegative integers.