Year	Number
1998	2.2414515003
1999	2.3312813611
2000	2.4191921709
2001	2.5090220317
2002	2.5398265377
2003	2.5706310438
2004	2.6014355498
2005	2.6322400558
2006	2.6514305652
2007	2.6706210747
2008	2.6898115841
2009	2.6638361987
2010	2.6378608133
2011	2.6118854279
2012	2.5630122756
2013	2.5141391233
2014	2.4652659709
2015	2.4163928186
2016	2.3675196663
2017	2.318646514
2018	2.2697733617
2019	2.2198185625
2020	2.2209002094