Year	Number
1961	1125
1962	1130
1963	1420
1964	1720
1965	1900
1966	2080
1967	2176
1968	2250
1969	2350
1970	2500
1971	2700
1972	2850
1973	3000
1974	3000
1975	3000
1976	3000
1977	3000
1978	3000
1979	3000
1980	3000
1981	3000
1982	3000
1983	3000
1984	3000
1985	3000
1986	3000
1987	3000
1988	3000
1989	3000
1990	3200
1991	3400
1992	3600
1993	3800
1994	4000
1995	4500
1996	5000
1997	5610
1998	5610
1999	8256