Year	Number
1971	11125
1972	13962
1973	11540
1975	14862
1976	12792
1977	13679
1978	13481
1979	13192
1980	13235
1981	13383
1982	13836
1983	13612
1984	13194
1985	13440
1986	13331
1987	13242
1988	13551
1989	14321
1990	14709
1991	15570
1992	16020
1993	16316
1994	16800
1995	17017
1996	17279
1997	17594
1998	17557
1999	14328
2000	14566
2001	15693
2002	14809
2003	15798
2004	15611
2005	16133
2006	16087
2007	15764
2008	16123
2009	15566
2010	15680
2011	15468
2012	14990
2013	14697
2014	16192
2015	15915
2016	16880
2017	16695
2018	18142
2019	18438
2020	18404