Cyclic prime number program generator
Java + Python 2, Score = (302 + 218) / 2 / 2 = 130

Here is a brief explanation on how this works: 


Choose a program and pick a positive integer, n; for Java, pass n as a command line argument; for Python, pass n through stdin. 


The program will then print a list of n primes followed by 2 newlines and then a snippet. 

Append this to a fresh copy of the program which was not chosen.
Choose a new n and pass it to this modified program


The program will then print a list of n primes followed by 2 newlines and then a snippet.

Append this to a fresh copy of the program which was originally chosen.
Rinse, repeat.




Golfed

Java, 302 bytes

Netbeans is able to compile this even with the A class missing, I haven't been able to figure out how. But once I do, I will add the flags to the byte count.

public class P{static int i=2;public static void main(String[]a){int l=2,n=Integer.parseInt(a[0]),x;String s="";try{new A().a();}catch(Exception e){}while(n&gt;0){if(i&gt;1){boolean b=false;for(x=2;x&lt;i;x++){if(i%x==0 &amp;&amp; i!=2)b=true;}if(!b){s+=s==""?i:","+i;l=i;n--;}i++;}}System.out.print(s+"\n\n+"+(l-1));}}


Python 2, 218 bytes

n=int(input())
s=[]
i=-1
while n:
 if i&gt;1:
  for x in range(2,i):
   if i%x==0and i!=2:break
  else:s+=[i];n-=1
  i+=1
 if n==0:print",".join(str(y)for y in s)+"\n\nclass A{void a(){P.i="+str(s[-1]+1)+";}}"
 if i&lt;0:i=2




Un-Golfed

Java

public class PPCG {

   public static int i = 2;

   public static void main(String[] args){
       int n = Integer.parseInt(args[0]);
       int last = 2;
       String s = "";
       try{
           new A().a();
       }catch(Exception e){}
       while(n&gt;0){
           if(i&gt;1){
               boolean broken=false;
               for(int x=2;x&lt;i;x++){
                   if(i%x==0 &amp;&amp; i!=2){
                       broken=true;
                   }
               }
               if(!broken){
                   s += s==""?i:","+i;
                   last = i;
                   n-=1;
               }
               i+=1;
           }
       }
       System.out.println(s+"\n\n+"+(last-1));
   }
}


Python 2

n=int(input())
s=[]
i=-1
while n:
  if i&gt;1:
    for x in range(2,i):
      if i%x==0 and i!=2:
        break
    else:
      s+=[i]
      n -= 1
    i+=1
  if n==0:
    print ",".join(str(y) for y in s)+"\n\nclass A{public static void a(){PPCG.i="+str(s[-1]-1)+";}}"
  if i&lt;0:
    i = 2


Update


-17 [16-12-13] Misc golfing