Year	Number
1987	1.6567375887
1988	1.7607039664
1989	1.8646703441
1990	1.9686367218
1991	2.0726030996
1992	2.1776201734
1993	2.2817966903
1994	2.3859732072
1995	2.4901497242
1996	2.5924349882
1997	2.6077541371
1998	2.6230732861
1999	2.638392435
2000	2.6529550827
2001	2.6680851064
2002	2.68321513
2003	2.6983451537
2004	2.7134751773
2005	2.7286052009
2006	2.7437352246
2007	2.9418439716
2008	3.1395271868
2009	3.337393617
2010	3.5352600473
2011	3.419178487
2012	3.3030969267
2013	3.1870153664
2014	3.0743262411
2015	3.0193853428
2016	3.1352245863
2017	3.1054373522
2018	1.4641127257
2019	1.4848084544
2020	1.4793042712