Year	Number
1961	2650
1962	2780
1963	2980
1964	3225
1965	3430
1966	3770
1967	3950
1968	3835
1969	4000
1970	4117
1971	4287
1972	4350
1973	4300
1974	4250
1975	4200
1976	4150
1977	4100
1978	3980
1979	3839
1980	3666
1981	3556
1982	3427
1983	3112
1984	3100
1985	3080
1986	3050
1987	3000
1988	3027
1989	3000
1990	2850
1991	2780
1992	2552
1993	2612
1994	2672
1995	2732
1996	2792
1997	2852
1998	2971
1999	2981
2000	2992
2001	3002
2002	3023
2003	3069
2004	3115
2005	3161
2006	3207
2007	3255