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  1. #include <iostream>
  2. #include <cmath>
  3.  
  4. int main()
  5. {
  6.     using namespace std ;
  7.  
  8.     //initialize some long ass integers
  9.     long long primeanswer = 1,p = 1,sqrt_of_i;
  10.     //flag for counting a discovery of a factor
  11.     int factorcount = 0;
  12.     //for loop counts down in twos from an odd number i is number to check
  13.     for (long long i=161;i>0; i=i-2)
  14.     {
  15.         //reset factor count flag to zero
  16.         factorcount =0;
  17.         //squaring i means that finding a factor of i wont take as long
  18.         sqrt_of_i = sqrt(i);
  19.         //loop usues p to get numbers fo checking against square of i
  20.         for(long long p=1; p<=sqrt_of_i; p++ )
  21.         {
  22.             //if there is a remainder of 0 when diveded...
  23.             if((i%p)==0)
  24.             {
  25.                 //then a factor has been found, the integer is incremented
  26.                 factorcount++;
  27.                 //if there is more than two factors the we are not dealing with a prime
  28.                 if(factorcount>=2)
  29.                     {
  30.                         break;
  31.                     }
  32.             }
  33.  
  34.         }
  35.         //if we found only one factor (1) then we output the prime :D
  36.         if(factorcount<=1)
  37.         {
  38.             primeanswer = i;
  39.                cout<<primeanswer<<" ";
  40.         }
  41.     }
  42.  
  43. }
  44.  
Success #stdin #stdout 0s 2852KB
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stdin
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Standard input is empty
stdout
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157 151 149 139 137 131 127 113 109 107 103 101 97 89 83 79 73 71 67 61 59 53 47 43 41 37 31 29 23 19 17 13 11 7 5 3 1
https://ideone.com/GxDpmr
language:
C++ (gcc 8.3)
created:
10 years ago
visibility:
public

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