Year	Number
1961	500
1962	550
1963	600
1964	650
1965	1000
1966	1300
1967	1600
1968	1800
1969	2350
1970	2900
1971	3450
1972	4000
1973	4550
1974	5100
1975	5650
1976	6200
1977	6750
1978	7300
1979	7850
1980	8400
1981	8950
1982	9500
1983	10050
1984	10600
1985	11150
1986	11700
1987	12250
1988	12800
1989	13350
1990	13900
1991	14450
1992	15000
1993	15550
1994	16100
1995	16650
1996	17200
1997	17750
1998	18300
1999	18850
2000	19400
2001	20006
2002	21000
2003	22000
2004	23000
2005	23000
2006	23999
2007	24800