Year	Number
1970	6700
1971	6800
1972	6800
1973	7000
1974	7600
1975	8400
1976	9700
1977	11600
1978	12500
1979	12500
1980	12900
1981	13400
1982	13300
1983	14600
1984	14700
1985	14200
1986	14300
1987	14300
1988	15000
1989	15600
1990	10000
1991	7200
1992	14300
1993	16200
1994	17200
1995	17900
1996	19400
1997	17200
1998	18700
1999	17300
2000	17486
2001	16682
2002	18929
2003	17833
2004	19512
2005	19142
2006	20673
2007	17685
2008	17999
2009	18191
2010	41848
2011	31753
2012	28814
2013	27305
2014	26610
2015	30073
2016	33387
2017	42782
2018	46450
2019	50959
2020	17004
2021	20436