在系列7，15，32…-yiteyi-C++库

给定一个系列7，15，32，…找出这个系列的第n项。

null

例如：

Input : 5Output : 138Input : 7Output : 568

建议：请在“上解决” 实践 “首先，在讨论解决方案之前。

方法： 通过观察序列的模式，我们可以很容易地确定它是一个混合序列。 S=7,15,32…。。序列中的每个元素都乘以2，然后比前一个元素多加一。 S=7,15（2*7+1），32（2*15+2）……。通过迭代，我们可以很容易地找到级数的第n项。

以下是上述方法的实施情况：

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

                         // 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.                       

Python3

                         # 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.                       

PHP

                         <?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.                       
                         ?>                       

Javascript

                         <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：

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