Hi,
For writing a file this is the code snippet
try {
BufferedWriter out = new BufferedWriter(new FileWriter("outfilename"));
out.write(char[] cbuf, int off, int len);
...

Hello,
You can ZIP the file as password protected. This would prompt with user-id and password.
Else you can use JAVA encryption, but this would not fully solve your requirement...

Aslan,
We would be happy if you can clearly give us full description of your problem.
Some clarifications sought:
Can r be 3? In that case how we need to proceed with the computation?

For n=25...