Year	Number
1970	21300
1971	20600
1972	17800
1973	18000
1974	17800
1975	15900
1976	14600
1977	13900
1978	15500
1979	17200
1980	19500
1981	13200
1982	13600
1983	12100
1984	11300
1985	11800
1986	8100
1987	11300
1988	14700
1989	15100
1990	17100
1991	12500
1992	11800
1993	13700
2010	21574
2011	18287
2012	16760
2013	26796
2014	24216
2015	24813
2016	24315
2017	9482
2018	14832
2019	13146
2021	14225