Triangular number
= Triangular number
{wiki=Triangular_number}
A triangular number is a figurate number that can form an equilateral triangle. The n-th triangular number is the sum of the first n natural numbers. This can be expressed mathematically as: \\\[ T_n = \\frac\{n(n + 1)\}\{2\} \\\] where \\( T_n \\) is the n-th triangular number and \\( n \\) is a positive integer.