Year	Number
2004-01-01	17
2005-01-01	17
2006-01-01	18
2007-01-01	20
2008-01-01	25
2009-01-01	26
2010-01-01	27
2011-01-01	31
2012-01-01	32
2013-01-01	31
2014-01-01	30
2015-01-01	30
2016-01-01	28