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Program to find N-th term of series 7, 21, 49, 91, 147, 217, …… in C++
In this problem, we are given a number n that denotes the nth term of the series. Our task is to create a program to find the N-th term of series 7, 21, 49, 91, 147, 217, …… in C++.
Problem Description - We will find the nth term of the series 7, 21, 49, 91, 147, 217, … and for that, we will deduce the general term of the series.
Let’s take an example to understand the problem,
Input − N = 5
Output − 147
Solution Approach:
Let’s deduce the general term of the given series. The series is −
7, 21, 49, 91, 147, 217, …
We can see that 7 is common here,
7 * (1, 3, 7, 13, 21, 31, ...)
Here, we can observe that this series is increasing like a square series. So,
Series: 7 * (12 , (22 - 1), (33 - 2), (42 - 3), (52 - 4), (62 - 5), ....)
The general term of the series can be generalized as −
Tn = 7*(n2 - (n-1))
Using the general term formula, we can find any value of the series.
For example,
T4 = 7*((4^2) - (4-1)) = 7(16 - 3) = 91 T7 = 7*((7^2) - (7-1)) = 7(49 - 6) = 301
Example
#include <iostream> using namespace std; int findNTerm(int N) { int nthTerm = ( 7*((N*N) - (N - 1)) ); return nthTerm; } int main() { int N = 9; cout<<N<<"th term of the series is "<<findNTerm(N); return 0; }
Output:
9th term of the series is 511
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