IEnumerable<int> filter(int p, IEnumerable<int> xs) {
     foreach(var j in xs)
      if (j % p > 0) yield return j;
    }
    
    IEnumerable<int> sieve(IEnumerable<int> s) {
     var p = s.First();
     yield return p;
     foreach(var e in sieve(filter(p,s.Skip(1))))
      yield return e;
    }
    
    var n = sieve(Enumerable.Range(2, 10000)).Skip(10).First();