Year Total 1960 0 1965 0 1970 0 1975 0 1976 0 1977 0 1978 0 1979 0 1980 0 1981 0 1982 0 1983 0 1984 0 1985 0 1986 0 1987 0 1988 0 1989 0 1990 0 1991 0 1992 0 1993 0 1994 1600 1995 2800 1996 3500 1997 4200 1998 5000 1999 6000 2000 103279 2001 417295 2002 701507 2003 1077000 2004 1530868 2005 2252508 2006 3135946 2007 4536000 2008 6160893 2009 8004120 2010 8636652 2011 10486614 2012 13108058 2013 15664666 2014 17039059 2015 18160667 2016 18717503 2017 19706027