Year	Number
1970	17388
1971	17493
1972	17619
1973	17671
1974	17718
1975	17785
1976	17890
1977	18051
1978	18204
1979	18441
1980	18831
1981	19069
1982	19425
1983	19790
1984	20235
1985	20799
1986	21287
1987	21681
1988	22373
1989	22761
1990	23066
1991	23135
1992	23100
1993	23043
1994	22343
1995	21237
1996	21080
1997	21070
1998	20977
1999	20628
2000	19914
2001	19230
2002	18514
2003	17872
2004	17298
2005	17007
2006	16821
2007	16724
2008	16579
2009	16426
2010	16085
2011	15628
2012	15059
2013	14570
2014	14070
2015	13606
2016	13219
2017	13042
2018	12867
2019	12762
2020	12638
2021	12508
2022	12413