Year	Number
1971	2768
1972	2696
1973	2963
1974	3083
1975	3159
1976	3329
1977	3505
1978	3690
1979	3893
1980	4010
1981	4130
1982	4284
1983	4364
1984	4268
1986	4718
1987	4544
1988	4563
1989	4226
1990	3581
1991	4004
2005	4653
2008	5827
2009	6427
2010	7553
2011	7974
2012	8267
2016	9756
2017	11334