Year	Number
1970	161000000
1971	175000000
1972	186000000
1973	196000000
1974	201000000
1975	208000000
1976	221000000
1977	239000000
1978	253000000
1979	263000000
1980	264000000
1981	264000000
1982	263000000
1983	267000000
1984	271000000
1985	269000000
1986	286000000
1987	292000000
1988	296000000
1989	297000000
1990	301000000
1991	309000000
1992	318000000
1993	329000000
1994	337000000
1995	347000000
1996	359000000
1997	368000000
1998	383000000
1999	392000000
2000	406000000
2001	418000000
2002	432000000
2003	445000000
2004	453000000
2005	459000000
2006	464000000
2007	470000000
2008	476000000
2009	478000000
2010	487000000
2011	495000000
2012	502000000
2013	509000000
2014	517000000
2015	521000000
2016	525000000
2017	526000000
2018	532000000