Year	Number
1960	15540
1961	15424
1962	15288
1963	15007
1964	14612
1965	14209
1966	13747
1967	13164
1968	12504
1969	11991
1970	11102
1971	10007
1972	8796
1973	7346
1974	5834
1975	3922
1976	1646
1977	-683
1978	-3324
1979	-6146
1980	-9135
1981	-12432
1982	-15706
1983	-19231
1984	-23253
1985	-27468
1986	-32143
1987	-37189
1988	-42393
1989	-48054
1990	-52723
1991	-56599
1992	-59634
1993	-61925
1994	-63700
1995	-65106
1996	-65800
1997	-65975
1998	-65616
1999	-64787
2000	-63610
2001	-62059
2002	-59876
2003	-57308
2004	-54383
2005	-50855
2006	-47174
2007	-43019
2008	-38736
2009	-34116
2010	-29330
2011	-24465
2012	-19946
2013	-16845
2014	-14265
2015	-12240
2016	-10887
2017	-9768
2018	-9106
2019	-8889
2020	-9117
2021	-10612
2022	-8000
2023	-8000