Year	Number
1973	13500
1974	13000
1975	14200
1976	13400
1977	13000
1978	13700
1979	14800
1980	13500
1981	13400
1982	13700
1983	14300
1984	11800
1985	13600
1986	15000
1987	15400
1988	13100
1989	14600
1990	13000
1991	13800
1992	14600
1993	15600
1994	13000
1995	12600
1996	13100
1997	12800
1998	11900
1999	5900
2000	6313
2001	6486
2002	6464
2003	7165
2004	7403
2005	7399
2006	7971
2007	11139
2008	11308
2009	16399
2010	19299.8261758691
2011	26535
2012	26996.2544120399
2013	59064
2014	65364
2015	55864
2016	59728
2017	70503
2018	53061
2019	68351
2020	42827.89
2021	50991