Year	Number
1981	6600
1982	6600
1983	6700
1984	7100
1985	4200
1986	3400
1987	3000
1988	3000
1989	3000
1990	2900
1991	2900
1992	2900
1993	2900
1994	2900
1995	3000
1996	3100
1997	3100
1998	3200
2017	5005
2018	5005
2019	4388
2020	3751.74
2021	3312.786