Year	Number
1970	6987074
1971	6643943
1972	7016295
1973	7440435
1974	7950124
1975	8167208
1976	8669035
1977	8985700
1978	9196914
1979	11200000
1980	11600000
1981	12100000
1982	12300000
1983	12700000
1984	14200000
1985	12900000
1986	16200000
1987	16600000
1988	16900000
1989	17100000
1990	17300000
1991	17300000
1992	17200000
1993	17400000
1994	18000000
1995	19000000
1996	20100000
1997	20500000
1998	21800000
1999	21700000
2000	20900000
2001	20800000
2002	19400000
2003	18800000
2004	20300000
2005	21400000
2006	23200000
2007	25200000
2008	26900000
2009	27800000
2010	28500000
2011	28400000
2012	27800000
2013	28500000
2014	26600000
2015	24700000
2016	23800000
2017	23200000
2018	23000000