Here the code for get three digit value 'n' and calculate r=2^n+1 then find that value 'r' is a prie or not, here i like store the integer value 'r' without exponential function and big Integer, please make a great help to me.
thanks in advance..


import java.*;
import java.io.*;
import java.io.IOException.*;
import java.math.*;


public class primenumber extends power{

public static void main(String a[])throws IOException {
//get input
power ob=new power();
DataInputStream dis=new DataInputStream(System.in);
System.out.println(" Enter three digit number n:");
String nu=dis.readLine();
int n=Integer.parseInt(nu);
long nvalue=ob.powerr(n);


//find prime
long r;
int primevalue=0,i,j=0;
long factors[]=new long[100];
for(i=2;i<=nvalue;i++)
{r=nvalue%i;

if(r==0)
{
if(i!=nvalue)
{factors[j]=i;
j++;
primevalue=1;
//System.out.println("not prime");
}//inner if
else
{
//System.out.println("prime");
}
}//outer if
}//for ends
System.out.println("Given number is"+n+"");
System.out.println("Prime calculation for"+nvalue+"");
System.out.println("power value is"+nvalue+"");

if(primevalue!=1){
System.out.println("The number "+nvalue+" is prime");
}
else{
System.out.println("The number "+nvalue+" is not a prime");
System.out.println("factors");
for(int k=0;k<=j-1;k++)
System.out.print("," +factors[k]);
}//primevalueif


}//main end here
}//class end here


class power {
//find power
final int two=2;
long powvalue=1 , i;
long powerr(int x){
int n=x;
for(i=1;i<=n+1;i++)
{powvalue*=two;
}
return powvalue;
};
}

try what? what are you stuck with? what is it supposed to do and what is it (not) doing?

could you be a bit more specific about these things?

Sample output:1
Enter three digit number n:
Given number is13
Prime calculation for16384
power value is16384
The number 16384 is not a prime
factors
,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192
BUILD SUCCESSFUL (total time: 9 seconds)

Sample output:2
run:
Enter three digit number n:
Given number is26
Prime calculation for134217728
power value is134217728
The number 134217728 is not a prime
factors
,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262144,524288,1048576,2097152,4194304,8388608,16777216,33554432,67108864
BUILD SUCCESSFUL (total time: 9 seconds)


if you give 31 (or) any big value as a input, system could not give output.Because prime calculation number "nvalue" will be a very big integer.

i gave 31 as an input and i got bug form system, please go through ..
Sample output:3
run:
Enter three digit number n:
Exception in thread "main" java.lang.ArithmeticException: / by zero
at primenumber.main(primenumber.java:40)
Java Result: 1
BUILD SUCCESSFUL (total time: 4 minutes 2 seconds)

if you are asked: enter a three-digit number, why do you only test with two-digit numbers? that Exception says that on line 40 of the code in your main class, you are dividing something by zero, which causes your exception

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