Year	Number
2004-01-01	2
2005-01-01	4
2006-01-01	6
2007-01-01	6
2008-01-01	7
2009-01-01	7
2010-01-01	10
2011-01-01	11
2012-01-01	13
2013-01-01	15
2014-01-01	17
2015-01-01	18