Fix formula for computing kurtosis (provided by

machinelearning.ru)

src/Numerics/Statistics/DescriptiveStatistics.cs

@@ -357,10 +357,8 @@ namespace MathNet.Numerics.Statistics
 
                     if (n > 3)
                     {
-                        Kurtosis = (((double)n * (n + 1))
-                                    / ((n - 1) * (n - 2) * (n - 3))
-                                    * (kurtosis / (Variance * Variance)))
-                                   - ((3.0 * (n - 1) * (n - 1)) / ((n - 2) * (n - 3)));
+                        Kurtosis = ((double)n * n - 1) / ((n - 2) * (n - 3))
+                            * (n * kurtosis / (variance * variance) - 3 + 6.0 / (n + 1));
                     }
                 }
             }