public static char toCloseByNumber(int number) {
		if (number > 20) {
			throw new IllegalArgumentException("Number must be [1-20]");
		}
		return (char) ('①' + number - 1);
	}
@Test
	public void toCloseByNumberTest(){
		assertEquals('②', CharUtil.toCloseByNumber(2));
		assertEquals('⑫', CharUtil.toCloseByNumber(12));
		assertEquals('⑳', CharUtil.toCloseByNumber(20));
	}