Year Number 1961 8000 1962 8100 1963 8200 1964 8400 1965 8611 1966 9000 1967 9400 1968 9800 1969 10132 1970 10700 1971 11600 1972 12622 1973 14048 1974 15601 1975 17552 1976 19785 1977 20056 1978 21632 1979 23887 1980 24684 1981 29712 1982 31084 1983 31586 1984 31299 1985 32000 1986 32800 1987 33500 1988 34278 1989 36700 1990 39155 1991 41000 1992 41000 1993 41000 1994 41000 1995 41000 1996 41000 1997 43226 1998 43226 1999 43226