Year	Number
1961	130
1962	150
1963	197
1964	357
1965	400
1966	450
1967	500
1968	550
1969	580
1970	620
1971	650
1972	690
1973	735
1974	900
1975	1000
1976	1100
1977	1300
1978	1500
1979	1700
1980	1900
1981	2100
1982	2400
1983	2700
1984	3000
1985	3400
1986	3900
1987	4400
1988	5000
1989	5600
1990	6500
1991	7100
1992	8000
1993	8600
1994	9300
1995	9469
1996	9500
1997	9600
1998	9792