function smallGamma2Series( a, x ) {
	var result;
	var apn;
	var n;
	var r;

	result = -x;
	x = -x;
	apn = a + 1.0;
	n = 1;
	return next;

	/**
	* Calculate the next term of the series.
	*
	* @private
	* @returns {number} series expansion term
	*/
	function next() {
		r = result / apn;
		result *= x;
		n += 1;
		result /= n;
		apn += 1.0;
		return r;
	}
}
Series representation for upper fraction when `z` is small.

@private
@param {number} a - function parameter
@param {number} x - function parameter
@returns {Function} series function