Year	Number
1961	3.0353469741257983
1962	3.4418878582232395
1963	3.847993939957739
1964	4.041031036296686
1965	4.320847373507823
1966	4.886196569561666
1967	5.413531792378521
1968	5.858357854004595
1969	6.326344203293707
1970	7.124897590191259
1971	7.121355892614706
1972	8.073803212723151
1973	10.153990113712647
1974	10.88840848260243
1975	11.782155703477075
1976	12.660629229102357
1977	13.5475995075913
1978	16.350314493464783
1979	18.340740079054914
1980	20.094892609878563
1981	22.517615055297895
1982	24.768331184134464
1983	26.44819405334693
1984	28.14961069093992