Year	Number
1970	20200
1971	20800
1972	21400
1973	22700
1974	23800
1975	22400
1976	23500
1977	21400
1978	22800
1979	23000
1980	22500
1981	19400
1982	15200
1983	19000
1984	13000
1985	11100
1986	8200
1987	8500
1988	11300
1989	6800
1990	10300
1991	9300
1992	10000
1993	9400
1994	9900
1995	10900
1996	9700
1997	10300
1998	10100
1999	10100
2000	10435
2001	10317
2002	10808
2003	10819
2004	11807
2005	12013
2006	11274
2007	12172
2008	12306
2009	13532
2010	19882
2011	21306
2012	21880
2013	23568
2014	23580
2015	24066
2016	24549
2017	25550
2018	25740
2019	26942
2020	9812
2021	13934