Definition:Triangular Number

Definition
Triangular numbers are those denumerating a collection of objects which can be arranged in the form of an equilateral triangle.

They are often denoted:
 * $T_1, T_2, T_3, \ldots$

Also known as
Triangular numbers are also known as triangle numbers.

Also see

 * Equivalence of Definitions of Triangular Number


 * Closed Form for Triangular Numbers: $T_n = \dfrac {n \left({n + 1}\right)} 2$