public double skewness() {
		double skewness = NaN;
		if (_n >= 3L) {
			final double var = _m2.value()/(_n - 1.0);
			skewness = var < 10E-20
				? 0.0d
				: (_n*_m3.value())/((_n - 1.0)*(_n - 2.0)*sqrt(var)*var);
		}

		return skewness;
	}
Return the skewness of values recorded, or {@code Double.NaN} if less
than two values have been recorded.

@see <a href="https://en.wikipedia.org/wiki/Skewness">Skewness</a>

@return the skewness of values, or {@code NaN} if less than two values
        have been recorded
jenetics/src/main/java/io/jenetics/stat/MomentStatistics.java