求数列 7、15、32 中的第 n 项，…
给定一个数列 7，15，32，…求这个数列的第 n 项。
示例:
Input : 5
Output : 138
Input : 7
Output : 568
进场:通过看系列的图案我们很容易识别出是一个混合系列。 S = 7，15，32….. 序列中的每个元素乘以 2，然后比前一个元素多加 1。 S = 7，15 (2 * 7 + 1)，32 (2 * 15 + 2)……。 利用迭代，我们可以很容易地找到级数的第 n 项。
下面是上述方法的实现:
C++
// CPP program to find nth term
#include <bits/stdc++.h>
using namespace std;
// utility function
int findTerm(int n)
{
if (n == 1)
return n;
else {
// since first element of the
// series is 7, we initialise
// a variable with 7
int term = 7;
// Using iteration to find nth
// term
for (int i = 2; i <= n; i++)
term = term * 2 + (i - 1);
return term;
}
}
// driver function
int main()
{
int n = 5;
cout << findTerm(n);
return 0;
}
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to find nth term
import java.lang.*;
class GFG {
// utility function
static int findTerm(int n)
{
if (n == 1)
return n;
else {
// since first element of the
// series is 7, we initialise
// a variable with 7
int term = 7;
// Using iteration to find nth
// term
for (int i = 2; i <= n; i++)
term = term * 2 + (i - 1);
return term;
}
}
// Driver code
public static void main(String[] args)
{
int n = 5;
System.out.print(findTerm(n));
}
}
// This code is contributed by Anant Agarwal.
Python 3
# Python3 program to find nth term
# utility function
def findTerm(n) :
if n == 1 :
return n
else :
# since first element of the
# series is 7, we initialise
# a variable with 7
term = 7
# Using iteration to find nth
# term
for i in range(2, n + 1) :
term = term * 2 + (i - 1);
return term;
# driver function
print (findTerm(5))
# This code is contributed by Saloni Gupta
C
// C# program to find nth term
using System;
class GFG {
// utility function
static int findTerm(int n)
{
if (n == 1)
return n;
else {
// since first element of the
// series is 7, we initialise
// a variable with 7
int term = 7;
// Using iteration to find nth
// term
for (int i = 2; i <= n; i++)
term = term * 2 + (i - 1);
return term;
}
}
// Driver code
public static void Main()
{
int n = 5;
Console.WriteLine(findTerm(n));
}
}
// This code is contributed by vt_m.
服务器端编程语言（Professional Hypertext Preprocessor 的缩写）
<?php
// PHP program to find nth term
// utility function
function findTerm($n)
{
if ($n == 1)
return $n;
else
{
// since first element of the
// series is 7, we initialise
// a variable with 7
$term = 7;
// Using iteration to find nth
// term
for ($i = 2; $i <= $n; $i++)
$term = $term * 2 + ($i - 1);
return $term;
}
}
// Driver Code
$n = 5;
echo(findTerm($n));
// This code is contributed by Ajit.
?>
java 描述语言
<script>
// Javascript program to find nth term
// utility function
function findTerm(n)
{
if (n == 1)
return n;
else
{
// since first element of the
// series is 7, we initialise
// a variable with 7
let term = 7;
// Using iteration to find nth
// term
for (let i = 2; i <= n; i++)
term = term * 2 + (i - 1);
return term;
}
}
// Driver Code
let n = 5;
document.write(findTerm(n));
// This code is contributed by gfgking.
</script>
输出:
138
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