It will be as the ancient Romans would have notated it MMLXXXXVIIII = 2099
The year with the longest Roman numerals in the 21st century is 1999, which is represented as "MCMXCIX." It has a total of eight Roman numerals in its representation.
Presumably you mean what date will have the most Roman numerals in the 21st century? If so then it will be December 31 2088 which will be: XII-XXXI-MMLXXXVIII actually, August 28, 2088 will be the most Roman Numerals in the 21st Century: VIII-XXVIII-MMLXXXVIII
October 21st, 2008 in Roman numerals is XXI.X.MMXVIII.
April 21st, 2008 is written as XXI.IV.MMVIII in Roman numerals.
In accordance with the modern rules now governing the Roman numerals system it will be the year of 2088 which in Roman numerals is written as MMLXXXVIII that will have the most numerals in it but if we were to write out 2099 in the same way that the ancient Romans once did then that would be even longer but instead we would now consider 2099 to be MMXCIX instead of its real original notation which once was MMLXXXXVIIII and could have been abridged to IMMC.QED
April 21, 2012 in Roman numerals is XXI.IV.MMXII.
Presumably you mean what date will have the most Roman numerals in the 21st century? If so then it will be December 31 2088 which will be: XII-XXXI-MMLXXXVIII actually, August 28, 2088 will be the most Roman Numerals in the 21st Century: VIII-XXVIII-MMLXXXVIII
October 21st, 2008 in Roman numerals is XXI.X.MMXVIII.
April 21st, 2008 is written as XXI.IV.MMVIII in Roman numerals.
In accordance with the modern rules now governing the Roman numerals system it will be the year of 2088 which in Roman numerals is written as MMLXXXVIII that will have the most numerals in it but if we were to write out 2099 in the same way that the ancient Romans once did then that would be even longer but instead we would now consider 2099 to be MMXCIX instead of its real original notation which once was MMLXXXXVIIII and could have been abridged to IMMC.QED
April 21, 2012 in Roman numerals is XXI.IV.MMXII.
The eclipse of July 22, 2009 will be the longest eclipse this century.
Xxi, vii, mmxii
The Roman numeral for 21 is XXI
XII/XXI/MCMLXXXV
The date February 21st 2009 can also be written as 02-21-2009 and in Roman numerals this would be II.XXI.MMIX
Yes, Roman numerals are still used in the 21st century, although their usage is primarily seen in specific contexts. For example, you may see them in movie titles (e.g., Rocky IV) or to denote years on buildings or clocks (e.g., MMXXI for 2021). They are also commonly used in the numbering of lists or sections in legal documents or academic papers.
21 July 1966 = 21.6.1966 = XXI.VI.MCMLXVI