Year	Number
1970	2449462
1971	3434297
1972	3608098
1973	3834499
1974	4109066
1975	4358607
1976	4576971
1977	4657628
1978	4804447
1979	5002314
1980	5455130
1981	6073716
1982	6067439
1983	6212350
1984	7497651
1985	8477245
1986	9570414
1987	10400000
1988	10900000
1989	11300000
1990	11500000
1991	11900000
1992	12200000
1993	12800000
1994	13800000
1995	15100000
1996	16300000
1997	16800000
1998	18100000
1999	19000000
2000	18500000
2001	18700000
2002	18000000
2003	17400000
2004	18800000
2005	19800000
2006	21600000
2007	23700000
2008	25700000
2009	26900000
2010	27700000
2011	27900000
2012	27600000
2013	29100000
2014	27400000
2015	25400000
2016	24500000
2017	24900000
2018	24900000