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# Program to print triangular number series till n

• Difficulty Level : Basic
• Last Updated : 16 Aug, 2022

A triangular number or triangle number counts objects arranged in an equilateral triangle, as in the diagram on the right. The n-th triangular number is the number of dots composing a triangle with n dots on a side, and is equal to the sum of the n natural numbers from 1 to n.

Examples :

```Input : 5
Output : 1 3 6 10 15

Input : 10
Output : 1 3 6 10 15 21 28 36 45 55

Explanation :
For k = 1 and j = 1 -> print k ( i.e. 1);
increase j by 1 and add into k then print k ( i.e  3 ) update k
increase j by 1 and add into k then print k ( i.e  6 ) update k
increase j by 1 and add into k then print k ( i.e 10 ) update k
increase j by 1 and add into k then print k ( i.e 15 ) update k
increase j by 1 and add into k then print k ( i.e 21 ) update k
.
.
and so on.```

Approach used is very simple. Iterate for loop till the value given n and for each iteration increase j by 1 and add it into k, which will simply print the triangular number series till n.
Below is the program implementing above approach:

## C

 `// C Program to find Triangular Number Series` `#include `   `// Function to find triangular number` `void` `triangular_series(``int` `n)` `{` `    ``int` `i, j = 1, k = 1;`   `    ``// For each iteration increase j by 1` `    ``// and add it into k` `    ``for` `(i = 1; i <= n; i++) {` `        ``printf``(``" %d "``, k);` `        ``j = j + 1; ``// Increasing j by 1` `        ``k = k + j; ``// Add value of j into k and update k` `    ``}` `}` `// Driven Function` `int` `main()` `{` `    ``int` `n = 5;` `    ``triangular_series(n);` `    ``return` `0;` `}`

## Java

 `// Java Program to print triangular number series till n` `import` `java.util.*;`   `class` `GFG {` `    `  `    ``// Function to find triangular number` `    ``static` `void` `triangular_series(``int` `n)` `    ``{` `        ``int` `i, j = ``1``, k = ``1``;` `     `  `        ``// For each iteration increase j by 1` `        ``// and add it into k` `        ``for` `(i = ``1``; i <= n; i++) {`   `            ``System.out.printf(``"%d "``, k);` `            ``j = j + ``1``; ``// Increasing j by 1` `            ``k = k + j; ``// Add value of j into k and update k` `        ``}` `    ``}` `    `  `    ``// Driver function ` `    ``public` `static` `void` `main(String[] args) ` `    ``{` `            ``int` `n = ``5``;` `            ``triangular_series(n);` `    ``}` `}` `        `  `// This code is contributed by Arnav Kr. Mandal.`

## Python3

 `# Python3 code to find Triangular ` `# Number Series`   `# Function to find triangular number` `def` `triangular_series( n ):` `    ``j ``=` `1` `    ``k ``=` `1` `    `  `    ``# For each iteration increase j ` `    ``# by 1 and add it into k` `    ``for` `i ``in` `range``(``1``, n ``+` `1``):` `        ``print``(k, end ``=` `' '``)` `        ``j ``=` `j ``+` `1` `# Increasing j by 1` `        `  `        ``# Add value of j into k and update k` `        ``k ``=` `k ``+` `j ` `        `  `# Driven Code` `n ``=` `5` `triangular_series(n)`   `# This code is contributed by "Sharad_Bhardwaj"`

## C#

 `// C# Program to print triangular` `// number series till n` `using` `System;`   `class` `GFG {` `    `  `    ``// Function to find triangular number` `    ``static` `void` `triangular_series(``int` `n)` `    ``{` `        ``int` `i, j = 1, k = 1;` `    `  `        ``// For each iteration increase j by 1` `        ``// and add it into k` `        ``for` `(i = 1; i <= n; i++) {`   `            ``Console.Write(k +``" "``);` `            ``j += 1; ``// Increasing j by 1` `            ``k += j; ``// Add value of j into k and update k` `        ``}` `    ``}` `    `  `    ``// Driver Code ` `    ``public` `static` `void` `Main() ` `    ``{` `            ``int` `n = 5;` `            ``triangular_series(n);` `    ``}` `}` `        `  `// This code is contributed by vt_m.`

## PHP

 ``

## Javascript

 ``

Output :

`1 3 6 10 15`

Time complexity : O(n)
Auxiliary Space : O(1), since no extra space has been taken.
Alternate Solution :
The solution is based on the fact that i-th Triangular number is sum of first i natural numbers, i.e., i * (i + 1)/2

## C

 `// C Program to find Triangular Number Series` `#include `   `// Function to find triangular number` `void` `triangular_series(``int` `n)` `{` `    ``for` `(``int` `i = 1; i <= n; i++) ` `        ``printf``(``" %d "``, i*(i+1)/2);` `}`   `// Driven Function` `int` `main()` `{` `    ``int` `n = 5;` `    ``triangular_series(n);` `    ``return` `0;` `}`

## Java

 `//Java program to print triangular number series till n` `import` `java.util.*;`   `class` `GFG {` `    `  `    ``// Function to find triangular number` `    ``static` `void` `triangular_series(``int` `n)` `    ``{` `        ``for` `(``int` `i = ``1``; i <= n; i++) ` `            ``System.out.printf(``"%d "``;, i*(i+``1``)/``2``);` `    ``}` `    `  `    ``// Driver function ` `    ``public` `static` `void` `main(String[] args) ` `    ``{` `            ``int` `n = ``5``;` `            ``triangular_series(n);` `    ``}` `}` `        `  `//This code is contributed by Arnav Kr. Mandal.`

## Python3

 `# Python3 code to find Triangular ` `# Number Series` ` `  `def` `triangular_series(n):` ` `  `     ``for` `i ``in` `range``(``1``, n ``+` `1``):` `         ``print``( i``*``(i``+``1``)``/``/``2``,end``=``' '``)` ` `  `# Driver code` `n ``=` `5` `triangular_series(n) ` `# This code is contributed by ihritik`

## C#

 `// C# program to print triangular` `// number series till n` `using` `System;`   `class` `GFG {` `    `  `    ``// Function to find triangular number` `    ``static` `void` `triangular_series(``int` `n)` `    ``{` `        ``for` `(``int` `i = 1; i <= n; i++) ` `            ``Console.Write(i * (i + 1) / 2 + ``" "``);` `    ``}` `    `  `    ``// Driver Code ` `    ``public` `static` `void` `Main() ` `    ``{` `            ``int` `n = 5;` `            ``triangular_series(n);` `    ``}` `}` `        `  `// This code is contributed by vt_m.`

## PHP

 ``

## Javascript

 ``

Output :

`1 3 6 10 15`

Time complexity : O(n)
Auxiliary Space : O(1) , since no extra space has been taken.

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