# JavaScript: Sequence number from the given Triangular Number

## JavaScript Math: Exercise-79 with Solution

Write a JavaScript program to get the number of dots based on the triangular number of the sequence.

From Wikipedia -A triangular number or triangle number counts objects arranged in an equilateral triangle. Triangular numbers are a type of figurate number, other examples being square numbers and cube numbers. The nth triangular number is the number of dots in the triangular arrangement with n dots on each side, and is equal to the sum of the n natural numbers from 1 to n. The sequence of triangular numbers, starting with the 0th triangular number, is

0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 120, 136, 153, 171, 190, 210, 231, 253, 276, 300, 325, 351, 378, 406, 435, 465, 496, 528, 561, 595, 630, 666...

**Test Data:**

(1) -> 1

(2) -> 3

(3) -> 6

(7) -> 28

(11) -> 66

**Sample Solution:**

**JavaScript Code:**

```
/**
* Function to calculate the triangular number.
* @param {number} n - The input number.
* @returns {number} - The triangular number.
*/
function test(n) {
// Calculate the triangular number using the formula (n * (n + 1)) / 2
return n * (n + 1) / 2;
}
// Test cases
// Assign value to n
n = 1;
// Print the value of n
console.log("Triangular number = " + n);
// Print the number of dots based on the triangular number of the sequence
console.log("Number of dots based on the triangular number of the sequence = " + test(n));
// Repeat the above steps for different values of n
n = 2;
console.log("Triangular number = " + n);
console.log("Number of dots based on the triangular number of the sequence = " + test(n));
n = 3;
console.log("Triangular number = " + n);
console.log("Number of dots based on the triangular number of the sequence = " + test(n));
n = 7;
console.log("Triangular number = " + n);
console.log("Number of dots based on the triangular number of the sequence = " + test(n));
n = 11;
console.log("Triangular number = " + n);
console.log("Number of dots based on the triangular number of the sequence = " + test(n));
```

Output:

Triangular number = 1 Number of dots based on the triangular number of the sequence = 1 Triangular number = 2 Number of dots based on the triangular number of the sequence = 3 Triangular number = 3 Number of dots based on the triangular number of the sequence = 6 Triangular number = 7 Number of dots based on the triangular number of the sequence = 28 Triangular number = 11 Number of dots based on the triangular number of the sequence = 66

**Flowchart: **

**Live Demo: **

See the Pen javascript-math-exercise-79 by w3resource (@w3resource) on CodePen.

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