How about this?

Adapted Code

1. void setup() {
2.   size(800, 800);
3.   background(0);
4.   strokeWeight(8);
5.   rectMode(CENTER);
6. }
7.  
8. void draw() {
9.   translate(width/2, height/2);
10.   noStroke();
11.   fill(0, 50);
12.   rect(0, 0, width, height);
13. }
14.  
15. void keyPressed() {
16.   int num = Character.getNumericValue(key);
17.   stroke(255, 170);
18.   float part = (float)TWO_PI/num;
19.   for (int i=0; i<num; i++) {
20.     pushMatrix();
21.     rotate(part*i);
22.     line(0, 0, 400, 0);
23.     popMatrix();
24.   }
25. }

nice one man, some neat little tricks there!

The main problem with your code is that you rotate too much. Rotate (like scale and translate) is cumulative and affects everything that comes after it. So either cumulatively rotate by small amounts or use push/popMatrix to rotate the full amount for the line. Also you use two ints which results in an int causing rounding errors at some point. Also you place rotate after line, instead of in front of it. Repairing all these issues will make your code work as well.

If you use this inside the for loops, your code will work as well...

1.         pushMatrix();
2.         stroke(255,170);
3.         rotate(radians(j*((float)360/numbers[i])));
4.         line(0,0,0,-350);
5.         popMatrix();