Year	Number
1970	18964
1971	19347
1972	19694
1973	19995
1974	20185
1975	20253
1976	20207
1977	20245
1978	20319
1979	20382
1980	20430
1981	20516
1982	20580
1983	20612
1984	20656
1985	20588
1986	20250
1987	19891
1988	19555
1989	19410
1990	19465
1991	19652
1992	19857
1993	20071
1994	20339
1995	20628
1996	20933
1997	21142
1998	21327
1999	21525
2000	21690
2001	21738
2002	21799
2003	21950
2004	21922
2005	21888
2006	21900
2007	21771
2008	21656
2009	21526
2010	21535
2011	21512
2012	21522
2013	21441
2014	21277
2015	21032
2016	20723
2017	20336
2018	20142
2019	19983
2020	19813
2021	19721
2022	19532