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Program to print triangular number series till n
• Difficulty Level : Basic
• Last Updated : 31 Oct, 2018

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.```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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

 ` `

Output :

```1 3 6 10 15
```

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

 ` `

Output :

```1 3 6 10 15
```

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