# Triangular number

The **triangular numbers** are the numbers which are the sum of the first natural numbers from to .

## Definition

The triangular number is the sum of all natural numbers from one to . That is, the triangle number is .

For example, the first few triangular numbers can be calculated by adding 1, 1+2, 1+2+3, ... etc.

```
$}
rowStart -= 0.5;
}
return 0;
```

}

for (int n=1; n<5; ++n) {

real value= n*(n+1)/2; draw_triangle((value+5,n),n); label( (string) value, (value+5, -2));

} </asy>$ (Error compiling LaTeX. ! Extra }, or forgotten $.)

## Formula

Using the sum of an arithmetic series formula, a formula can be calculated for :

The formula for finding the triangular number can be written as .

It can also be expressed as the sum of the row in Pascal's Triangle and all the rows above it. Keep in mind that the triangle starts at Row 0.

*This article is a stub. Help us out by expanding it.*