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Program to check if N is a Octadecagon number
• Last Updated : 23 Mar, 2021

Given a number N, the task is to check if N is a Octadecagon Number or not. If the number N is an Octadecagon Number then print “Yes” else print “No”.

Octadecagon Number is a 18-sided polygon. The first few Octadecagon Numbers are 1, 18, 51, 100, 165, 246, 343, …

Examples:

Input: N = 18
Output: Yes
Explanation:
Second Octadecagon number is 18.
Input: N = 30
Output: No

Approach:

1. The Kth term of the Octadecagon number is given as 2. As we have to check that the given number can be expressed as a Octadecagon Number or not. This can be checked as:

=> => 1.
2. If the value of K calculated using the above formula is an integer, then N is a Octadecagon Number.
3. Else N is not a Octadecagon Number.

Below is the implementation of the above approach:

## C++

 // C++ program for the above approach#include using namespace std; // Function to check if N is a// Octadecagon Numberbool isOctadecagon(int N){    float n        = (14 + sqrt(128 * N + 196))          / 32;     // Condition to check if the    // number is a Octadecagon number    return (n - (int)n) == 0;} // Driver Codeint main(){    // Given Number    int N = 18;     // Function call    if (isOctadecagon(N)) {        cout << "Yes";    }    else {        cout << "No";    }    return 0;}

## Java

 // Java program for the above approachimport java.lang.Math; class GFG{     // Function to check if N is a// octadecagon Numberpublic static boolean isOctadecagon(int N){    double n = (14 + Math.sqrt(128 * N +                               196)) / 32;         // Condition to check if the    // number is a octadecagon number    return (n - (int)n) == 0;} // Driver Code   public static void main(String[] args){             // Given Number    int N = 18;         // Function call    if (isOctadecagon(N))    {        System.out.println("Yes");    }    else    {        System.out.println("No");    }}} // This code is contributed by divyeshrabadiya07

## Python3

 # Python3 program for the above approachimport math # Function to check if N is a# octadecagon numberdef isOctadecagon(N):     n = (14 + math.sqrt(128 * N + 196)) // 32         # Condition to check if the    # number is a octadecagon number    return ((n - int(n)) == 0) # Driver codeif __name__=='__main__':         # Given number    N = 18         # Function Call    if isOctadecagon(N):        print('Yes')    else:        print('No') # This code is contributed by rutvik_56

## C#

 // C# program for the above approachusing System;class GFG{     // Function to check if N is a// octadecagon Numberpublic static bool isOctadecagon(int N){    double n = (14 + Math.Sqrt(128 * N +                               196)) / 32;         // Condition to check if the    // number is a octadecagon number    return (n - (int)n) == 0;} // Driver Codepublic static void Main(String[] args){             // Given Number    int N = 18;         // Function call    if (isOctadecagon(N))    {        Console.WriteLine("Yes");    }    else    {        Console.WriteLine("No");    }}} // This code is contributed by 29AjayKumar

## Javascript

 
Output:
Yes

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