Year	Number
1965	3900
1966	3900
1967	3900
1968	3900
1969	3900
1970	4900
1971	4900
1972	4900
1973	4900
1974	4900
1975	5600
1976	6299
1977	6518
1978	6936
1979	7693
1980	8492
1981	8882
1982	8963
1983	9545
1984	9751
1985	10159
1986	10303
1987	10905
1988	15010
1989	15768
1990	15852
1991	16905
1992	17915
1993	19177
1994	20553
1995	21410
1996	22000
1997	22000
1998	22000
1999	22000
2000	22000
2001	22000
2002	22000
2003	7000
2004	13820
2005	15907
2006	13754
2007	13404
2008	9050
2009	11600
2010	13400
2011	14200
2012	14932
2013	15679
2014	16300
2015	17000
2016	17000
2017	17000
2019	17000
2020	17000