# Icosihenagonal Number

Last Updated : 17 Mar, 2021

Given a number N, the task is to find Nth Icosihenagonal number.

An Icosihenagonal number is class of figurate number. It has 21 â€“ sided polygon called Icosihenagon. The n-th Icosihenagonal number counts the 21 number of dots and all others dots are surrounding with a common sharing corner and make a pattern. The first few Icosihenagonal numbers are 1, 21, 60, 118, 195, 291, 406 …

Examples:

Input: N = 2
Output: 21
Explanation:
The second Icosihenagonal number is 21
Input: N = 6
Output: 291

Approach: In mathematics, the Nth Icosihenagonal number is given by the formula:

Below is the implementation of the above approach:

## C++

 // C++ program to find nth// Icosihenagonal number #include using namespace std; // Function to find// Icosihenagonal numberint Icosihenagonal_num(int n){    // Formula to calculate nth    // Icosihenagonal number    return (19 * n * n - 17 * n) / 2;} // Driver Codeint main(){    int n = 3;    cout << Icosihenagonal_num(n) << endl;     n = 10;    cout << Icosihenagonal_num(n) << endl;     return 0;}

## Java

 // Java program to find nth// Icosihenagonal numberclass GFG{ // Function to find// Icosihenagonal numberstatic int Icosihenagonal_num(int n){    // Formula to calculate nth    // Icosihenagonal number    return (19 * n * n - 17 * n) / 2;} // Driver Codepublic static void main(String[] args){    int n = 3;    System.out.print(Icosihenagonal_num(n) + "\n");     n = 10;    System.out.print(Icosihenagonal_num(n) + "\n");}} // This code is contributed by Rajput-Ji

## Python3

 # Python3 program to find nth # icosihenagonal number  # Function to find # icosihenagonal number def Icosihenagonal_num(n):         # Formula to calculate nth     # icosihenagonal number    return (19 * n * n - 17 * n) / 2     # Driver Coden = 3print(int(Icosihenagonal_num(n))) n = 10print(int(Icosihenagonal_num(n))) # This code is contributed by divyeshrabadiya07

## C#

 // C# program to find nth// Icosihenagonal numberusing System; class GFG{ // Function to find// Icosihenagonal numberstatic int Icosihenagonal_num(int n){    // Formula to calculate nth    // Icosihenagonal number    return (19 * n * n - 17 * n) / 2;} // Driver Codepublic static void Main(){    int n = 3;    Console.Write(Icosihenagonal_num(n) + "\n");     n = 10;    Console.Write(Icosihenagonal_num(n) + "\n");}} // This code is contributed by Code_Mech

## Javascript

 

Output:
60
865

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