Program to print triangular number series till n - GeeksforGeeks

19 Mar, 2021
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
Java
Python3
C#
PHP
Javascript
// C Program to find Triangular Number Series#include <stdio.h> // Function to find triangular numbervoid 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 Functionint main(){    int n = 5;    triangular_series(n);    return 0;}
// Java Program to print triangular number series till nimport 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 code to find Triangular# Number Series # Function to find triangular numberdef 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 Coden = 5triangular_series(n) # This code is contributed by "Sharad_Bhardwaj"
// C# Program to print triangular// number series till nusing 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// PHP Program to find// Triangular Number Series // Function to find// triangular numberfunction triangular_series($n){    $i; $j = 1; $k = 1;     // For each iteration increase j    // by 1 and add it into k    for ($i = 1; $i <= $n; $i++)    {        echo(" " . $k . " ");                 // Increasing j by 1        $j = $j + 1;                 // Add value of j into k and update k        $k = $k + $j;    }} // Driver Code$n = 5;triangular_series($n); // This code is contributed by Ajit.?>
<script>// javascript Program to find Triangular Number Series // Function to find triangular numberfunction triangular_series( n){    let i, j = 1, k = 1;     // For each iteration increase j by 1    // and add it into k    for (i = 1; i <= n; i++)    {        document.write(k+" ");        j = j + 1; // Increasing j by 1        k = k + j; // Add value of j into k and update k    }} // Driven Function    let n = 5;    triangular_series(n);        // This code is contributed by Rajput-Ji </script>
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
Java
Python3
C#
PHP
Javascript
// C Program to find Triangular Number Series#include <stdio.h> // Function to find triangular numbervoid triangular_series(int n){    for (int i = 1; i <= n; i++)        printf(" %d ", i*(i+1)/2);} // Driven Functionint main(){    int n = 5;    triangular_series(n);    return 0;}
//Java program to print triangular number series till nimport 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 code to find Triangular# Number Series  def triangular_series(n):       for i in range(1, n + 1):         print( i*(i+1)//2,end=' ')  # Driver coden = 5triangular_series(n)# This code is contributed by ihritik
// C# program to print triangular// number series till nusing 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// PHP Program to find// Triangular Number Series // Function to find// triangular numberfunction triangular_series($n){    for ($i = 1; $i <= $n; $i++)        echo(" " . $i * ($i + 1) /                         2 . " ");} // Driver Code$n = 5;triangular_series($n); // This code is contributed by Ajit.?>
<script>// javascript Program to find Triangular Number Series // Function to find triangular numberfunction triangular_series( n){    for (let i = 1; i <= n; i++)       document.write(" "+ i * (i + 1)/2);} // Driven Function    let n = 5;    triangular_series(n);         // This code is contributed by gauravrajput1</script>
Output :  
1 3 6 10 15
 
jit_t
ihritik
Rajput-Ji
GauravRajput1
series
triangular-number
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series
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