the resultants of the if statement condition does not seem to be inside my vector array

I would like this program to display each value of n, multiplied by the variable currentprimenumber to be pushed into the all_numbers vector array and then for each integer in the vector array to be displayed. To be honest with you, I cant figure out what to put in the code statement

std::cout<< "something to display the vector elements here"<<std::endl;

I tried a few things already like

std::cout << n << std::endl;  
// i get the numbers from 3 o 49 but they arent multiplied to the currentprimenumber, thats the issue :(

std::cout << all_numbers.size() << std::endl; // but i got a list of ones 

std::cout << all_numbers[n] << std::endl;  // i got Debugger assertion failed 

Then I tried toggling with the brackets to see if its a scope issue I ran to here because at this point I was making the same mistakes all over again Heres my code below

 int main(){                
        for (int n = 3; n < 50; n++) { 
             int currentprimenumber = 2;
             std::vector<int>all_numbers;
        if (n*currentprimenumber) 
             all_numbers.push_back(n);
        for (int n : all_numbers)
             std::cout << n << std::endl;
                     //} // if(n*currentprimenumber)
                 }//for (int n = 3; n < 50; n++)
          } // int main()`