Cool thats kind of how mine started but it wasn't slowed down by interface. I have lots of other things to do but I'll have a thought to that end to.

I also have made a version which checks the powers of two -1 here is the code.

PrintWriter output;
long x=1;
long lastprime;
PFont font;
boolean prime=true;
int pps;
float framerate=50;
long truex;

void setup()
{
 size(720,200);
 font = loadFont("Algerian-48.vlw");
 textFont(font, 48);
 frameRate(framerate);
 output = createWriter("data/primes.txt");
 long counter=0;
}

void draw()
{
 delay(int(frameRate/5));
 setup_primes();
 test_primes();
   display_primes();
 save_primes();
}

void setup_primes()
{
 background(0);
 x++;
 prime=true;
}

void test_primes()
{
 truex++;
 truex=(truex*2)-1;
 long counter;
 long countdif;
 counter=1;
 while(counter<truex/2)
 {
   countdif=truex/counter;
   counter++;
   if (countdif==0)
   {
     prime=false;
   }
 }
 if ((prime)&&(truex>0))
 {
    output.println("x"+str(x));
     output.println("truex"+str(truex));
   lastprime=x;
 }
}

void display_primes()
{
 text("last prime:"+lastprime+"  FPS:"+int(frameRate),20,60);
 text("checking:2^"+x+"-1",20,120);
 text("truex:"+truex,20,180);
}

void save_primes()
{
   output.flush();
}