Year	Number
1971	8500
1972	9000
1973	9500
1974	10000
1975	10500
1976	11000
1977	12000
1978	12000
1979	13000
1980	13300
1981	13300
1982	13300
1983	13300
1984	13400
1985	13700
1986	13700
1987	13700
1988	27600
1989	14000
1990	14000
1991	14000
1992	14000
1993	14000
1994	14000
1995	14700
1996	14700
1997	20900
1998	20800
2010	25969.3823646158
2011	130197.6
2012	316620.85
2013	401712
2014	303024
2015	400758
2016	458222
2017	496322
2018	404301.328013225
2019	425475
2020	138898
2021	31268