Year	Number
1970	12100000
1971	13100000
1972	13500000
1973	13700000
1974	14000000
1975	14000000
1976	14500000
1977	14700000
1978	14900000
1979	15200000
1980	15500000
1981	15800000
1982	15900000
1983	15900000
1984	15800000
1985	16000000
1986	16400000
1987	16500000
1988	16400000
1989	16400000
1990	16200000
1991	16400000
1992	16500000
1993	17300000
1994	18200000
1995	18200000
1996	18200000
1997	17100000
1998	15200000
1999	15400000
2000	14300000
2001	14400000
2002	14100000
2003	13800000
2004	15000000
2005	15200000
2006	14200000
2007	14200000
2008	13900000
2009	13700000
2010	13800000
2011	13400000
2012	13100000
2013	14600000
2014	14400000
2015	14000000
2016	13900000
2017	14000000
2018	14000000