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A triangular number, sometimes called triangle number, is a figurate number that looks like an equilateral triangle or a right triangle.

For example the number 6 is a triangular number since you can use 6 dots and arrange the dots until the figure you get looks like an equilateral triangle or a right triangle.

The first triangular number is 1

The second triangular number is 3

The third triangular number is 6

The third triangular number is 15

To find the nth triangular number, use the formula below:

[n(n+1)] ÷ 2

For example, to find the third triangular number, just substitute 3 for n in [n(n+1)] ÷ 2

[3(3+1)] ÷ 2 = [3(4)] ÷ 2 = [12] ÷ 2 = 6