Year	Number
1975	18800
1976	18900
1977	18100
1978	20400
1979	20300
1980	19200
1981	19100
1982	19400
1983	18300
1984	55400
1985	53900
1986	57300
1987	64700
1988	69500
1989	71400
1990	62400
1991	56700
1992	53200
1993	24700
1994	57800
1995	26800
1996	26800
1997	29300
1998	29600
1999	27100
2000	27512
2001	29826
2002	31147
2003	17704
2004	18712
2005	19606
2006	21935
2007	21700
2008	21751
2009	21450
2010	32741
2011	36364.3197806363
2012	37309.857693979
2013	30012
2014	34068
2015	51680
2016	48892
2017	53696
2018	41173
2019	54328
2020	36664
2021	34007