Program to print the Sum of series -1 + 2 + 11 + 26 + 47 +…..
Given a number N, the task is to find the sum of first N number of series:
-1, 2, 11, 26, 47, 74, …..
Examples:
Input: N = 3
Output: 12
Explanation:
Sum = (N * (N + 1) * (2 * N - 5) + 4 * N) / 2
= (3 * (3 + 1) * (2 * 3 - 5) + 4 * 3) / 2
= 12
Input: N = 9
Output: 603
Approach:
The Nth term of the given series can be generalised as:
Nth term of the series 
Below is the implementation of the above approach:
C++
// CPP program to find SUM // upto N-th term of the series: // -1, 2, 11, 26, 47, 74, ..... #include <iostream> using namespace std; // calculate Nth term of series int findSum(int N) { return (N * (N + 1) * (2 * N - 5) + 4 * N) / 2; } // Driver Function int main() { // Get the value of N int N = 3; // Get the sum of the series cout << findSum(N) << endl; return 0; } |
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Java
// Java program to find SUM // upto N-th term of the series: // -1, 2, 11, 26, 47, 74, ..... import java.util.*; class solution { static int findSum(int N) { return (N * (N + 1) * (2 * N - 5) + 4 * N) / 2; } //driver function public static void main(String arr[]) { // Get the value of N int N = 3; // Get the sum of the series System.out.println(findSum(N)); } } //THis code is contributed by //Surendra_Gangwar |
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Python3
# Python3 program to find sum # upto N-th term of the series: # -1, 2, 11, 26, 47, 74, ..... # calculate Nth term of series def findSum(N): return ((N * (N + 1) * (2 * N - 5) + 4 * N) / 2) #Driver Function if __name__=='__main__': #Get the value of N N = 3 #Get the sum of the series print(findSum(N)) #this code is contributed by Shashank_Sharma |
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C#
// C# program to find SUM // upto N-th term of the series: // -1, 2, 11, 26, 47, 74, ..... using System; class GFG { static int findSum(int N) { return (N * (N + 1) * (2 * N - 5) + 4 * N) / 2; } // Driver Code static public void Main () { // Get the value of N int N = 3; // Get the sum of the series Console.Write(findSum(N)); } } // This code is contributed by Raj |
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PHP
<?php // PHP program to find SUM // upto N-th term of the series: // -1, 2, 11, 26, 47, 74, ..... // calculate Nth term of series function findSum($N) { return ($N * ($N + 1) * (2 * $N - 5) + 4 * $N) / 2; } // Driver Code // Get the value of N $N = 3; // Get the sum of the series echo findSum($N) . "\n"; // This code is contributed // by Akanksha Rai(Abby_akku) ?> |
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Output:
12
Time Complexity: O(1)
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