Year	Number
1961	3.654236147574519
1962	3.8882940159500308
1963	3.9654147834883418
1964	4.086752145016941
1965	4.220651234293749
1966	4.687230660439525
1967	5.01893721097641
1968	5.323249028351849
1969	5.74754663517581
1970	6.331584397056708
1971	6.569488439559781
1972	7.514845605700713
1973	7.819394404920841
1974	8.490680607319472
1975	8.97307451471509
1976	10.06275820744899
1977	11.595130071482195
1978	12.777318687224966
1979	14.02316073899067
1980	14.723127896644105
1981	16.39615541705488
1982	17.123455042676607
1983	18.795316697359308
1984	19.53623317230863
1985	19.450264096555507
1986	20.67925663908297
1987	22.203340829790047
1988	23.901507005158415
1989	25.530721790044606
1990	27.06704833678435
1991	27.098394105552202
1992	32.52217968141694
1993	31.765742911108195
1994	31.212621553316943
1995	33.8753287250887
1996	34.9600401343681