Year	Number
1970	35596040
1971	36233100
1972	35479168
1973	33199174
1974	32865806
1975	32371376
1976	32051500
1977	32018104
1978	33740472
1979	33136316
1980	32236328
1981	30967784
1982	30268528
1983	29855558
1984	29556180
1985	28787100
1986	27997792
1987	27722894
1988	26440126
1989	25123396
1990	26134696
1991	25843332
1992	26303740
1993	26755164
1994	27794416
1995	30247068
1996	32138070
1997	33451818
1998	31659136
1999	28740556
2000	26880860
2001	25935932
2002	25622516
2003	24355970
2004	22550740
2005	20903880
2006	21568308
2007	17780800
2008	18841372
2009	19972968
2010	20400000
2011	21100000
2012	19900000
2013	19200000
2014	18500000
2015	18600000
2016	17900000
2017	17600000
2018	16900000