Triangular numbers are a sequence of numbers that can form an equilateral triangle when represented as dots. The first few triangular numbers are 1, 3, 6, 10, and 15. Each number is the sum of the natural numbers up to a certain point. For example, 6 is the sum of 1 + 2 + 3. The formula to find the nth triangular number is T_n = \fracn(n + 1)2 . This means that to find the 4th triangular number, you would calculate T_4 = \frac4(4 + 1)2 = 10 . Triangular numbers have applications in various fields, including mathematics and combinatorics.