Year	Number of
1969	12960
1970	13420
1971	13980
1972	14660
1973	15350
1974	15970
1975	16460
1976	16630
1977	16790
1978	16910
1979	17080
1980	17360
1981	17700
1982	18040
1983	18530
1984	19090
1985	19660
1986	20100
1987	20560
1988	21050
1989	21570
1990	22090
1991	22340
1992	22640
1993	22910
1994	23120
1995	23470
1996	23680
1997	24000
1998	24350
1999	24630
2000	24850
2001	24840
2002	24740
2003	24610
2004	24480
2005	24420
2006	24360
2007	24320
2008	24300
2009	24350
2010	24400
2011	24450
2012	24590
2013	24810
2014	25020
2015	25500