function tgammaSmallUpperPart( a, x, invert ) {
	var initialValue;
	var result;
	var pgam;
	var p;
	var s;

	result = gamma1pm1( a );
	pgam = ( result + 1.0 ) / a;
	p = powm1( x, a );
	result -= p;
	result /= a;
	s = smallGamma2Series( a, x );
	p += 1.0;
	initialValue = ( invert ) ? pgam : 0.0;
	result = -p * sumSeries( s, {
		'initialValue': (initialValue - result) / p
	});
	if ( invert ) {
		result = -result;
	}
	return [ result, pgam ];
}
Compute the full upper fraction (Q) when `a` is very small.

@private
@param {number} a - function parameter
@param {number} x - function parameter
@param {boolean} invert - boolean indicating if the upper tail of the incomplete gamma function should be evaluated
@returns {Array} full upper fraction (Q) and pgam