Year	Number
1971	4622
1972	5905
1973	6422
1974	6210
1975	7971
1976	12562
1977	16244
1978	18905
1979	22668
1980	27264
1981	32362
1982	39868
1983	45957
1984	51892
1985	56733
1986	62082
1987	68259
1988	76404
1989	85586
1990	95669
1991	107881
1992	118011
1993	129683
1994	145143
1995	159840
1997	180764
1998	190576
2016	441510
2017	528480
2019	556259
2020	675864