Year	Number
1970	1600
1971	1500
1972	1200
1973	1300
1974	1300
1975	1400
1976	1600
1977	1500
1978	1600
1979	1600
1980	2300
1981	2200
1982	2300
1983	2300
1984	2300
1985	2400
1986	3600
1987	2700
1988	2800
1989	2800
1990	2200
1991	2900
1992	2800
1993	3000
1994	3000
1995	3100
1996	3300
1997	1800
1998	1800
1999	3300
2000	3368
2001	1983
2002	1257
2003	1285
2004	1415
2005	1471
2006	1512
2007	1614
2008	1413
2009	1433
2010	4235
2011	3983.15025906736
2012	3856.22456300177
2013	3780
2014	3672
2015	3875
2016	3861
2017	3863
2018	3988
2019	4105
2020	1790
2021	3007