function finiteHalfGammaQ( a, x ) {
	var half;
	var term;
	var sum;
	var e;
	var n;

	e = erfc( sqrt(x) );
	if ( e !== 0 && a > 1.0 ) {
		term = exp( -x ) / sqrt( PI * x );
		term *= x;
		half = 0.5;
		term /= half;
		sum = term;
		for ( n = 2; n < a; ++n ) {
			term /= n - half;
			term *= x;
			sum += term;
		}
		e += sum;
	}
	return e;
}
Calculates normalized Q when a is a half-integer.

@private
@param {number} a - function parameter
@param {number} x - function parameter
@returns {number} upper gamma fraction