Finding factorials using regex: .NET balancing groups

Believe it or not, this is also a first iteration solution. In fact, as a personal first, this pattern was completely developed on paper (see also on ideone.com).

var r = new Regex(@"(?xn) 

^(
   (
     ( ^.
     | (?=  (?<temp-n> .)+ )
       (?<= (?<fact>  .+)  )
       (?<n-temp> \k<fact> )+?
       (?(temp) (?!))
     )
     (?<n>)
   )+
 )$

");

for (int x = 0; x < 6000; x++) {
   Match m = r.Match("".PadLeft(x));
   if (m.Success) {
      Console.WriteLine("{0,4} = {1}! ", x, m.Groups["n"].Captures.Count);
   }
}

The only thing that tripped me up was the need for reluctant quantifier, but everything else was exactly as it was first written on paper.

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I'm halfway convinced that the problem with the greedy repetition is a bug, or perhaps was and has since been fixed (see: stackoverflow - Backtracking a balancing group in a greedy repetition may cause imbalance?)