Google_Sheet_Helpers::num2alpha( $n )

Convert number to corresponding excel range.

	public function num2alpha( $n ) {
		for ( $r = ''; $n >= 0; $n = intval( $n / 26 ) - 1 ) {
			$r = chr( $n % 26 + 0x41 ) . $r;
		}
		return $r;
	}