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.

Some sources refer to a triangular number just as a triangular.

Also see

 * Equivalence of Definitions of Triangular Number


 * Closed Form for Triangular Numbers: $T_n = \dfrac {n \paren {n + 1} } 2$


 * Definition:Polygonal Number:
 * Definition:Square Number
 * Definition:Pentagonal Number
 * Definition:Hexagonal Number