In the second line of the while loop, you have to declare the variable, so : for (int i=0; ...etc ; ...etc)
You also have some misplaced curly braces. :)

I can't actually help with the math parts. ;)

why would i be getting an unexpected "TOKEN :)" in the FOR LOOP line? I am really trying to get this right but I am not experienced enough to know the proper semantics at this point to do this without a little help. I think i solved the curly brace problem though by opening up the code and making it more readable.


int prime_counter = 0;
int current_odd_number = 0;
int divisor_tester = 0;

void setup() {
  size(500,500);
  background(255);
 
}

void draw() {
 
 while (prime_counter < 1000) {
  
  for (int i = 0; < int(sqrt(current_odd_number)); i = i + 1)
 
  {
    if (current_odd_number) % i == 0)
   
    {
      current_odd_number = current_odd_number + 2
    }  else if {
      (current_odd_number) % i != 0 && i < (int(sqrt(current_odd_number)))
    {
      i++
     
    } else {
    prime_counter = prime_counter + 1;
    current_odd_number = current_odd_number + 2;
    println(current_odd_number + "is prime" + prime_counter);
  }
}
}

Your code is still riddled with syntax errors! Here's an attempt and just cleaning those up:

" I am not experienced enough to know the proper semantics at this point to do this without a little help"
The proper semantics is explained in the tutorials, the reference, and seen in the examples...

Some additional remarks:
int prime_counter = 0;
int current_odd_number = 0;
int divisor_tester = 0;

void setup() {
  size(500,500);
  background(255);
 
}

void draw() { // Why is this in draw? You don't want to repeat the computation on each frame!
 
 while (prime_counter < 1000) {
  
  for (int i = 0; i < int(sqrt(current_odd_number)); i = i + 1) // You can use the i++ shortcut.
  // changing the loop target in the loop is a recipe for disaster...
  {
    if (current_odd_number) % i == 0)
   
    {
      current_odd_number = current_odd_number + 2 // Shortcut: current_odd_number += 2;
    }  else if {
      // You are in the else, so you are sure the first test is OK. And why reevaluate the test on i?
      (current_odd_number) % i != 0 && i < (int(sqrt(current_odd_number)))
    {
      // This condition makes me think you really want a while loop, not a for one, since you evaluate its terms inside the loop
      i++
     
    } else {
    // Looks like this part is never evaluated
    prime_counter = prime_counter + 1;
    current_odd_number = current_odd_number + 2;
    println(current_odd_number + "is prime" + prime_counter);
  }
}
}