Year	Number
1970	10700
1971	11300
1972	12500
1973	13800
1974	13800
1975	14600
1976	13200
1977	14200
1978	14500
1979	14800
1980	15000
1981	15000
1982	16400
1983	15800
1984	16200
1985	18000
1986	16700
1987	18600
1988	18400
1989	17600
1990	18300
1991	17700
1992	16900
1993	17300
1994	18700
1995	19200
1996	21600
1997	21100
1998	21700
1999	14700
2000	12589
2001	11728
2002	9989
2003	9750
2004	10832
2005	11803
2006	12785
2007	14064
2008	12431
2009	12924
2010	21668.3164735801
2011	24488
2012	26469
2013	26643
2014	28979
2015	35558
2016	41022
2017	50389
2018	54653.3025910987
2019	35823
2020	13594
2021	24518