D5
DIV
D + IV (roman numeral 4)
D + IIII
http://mathtourist.blogspot.com/2010/08/iiii-versus-iv-on-clocks.html
You can also count up how many of each character you need to create all the numbers. In the IIII case, the totals are 20 I's, 4 V's, and 4 X's (all even numbers), versus 17 I's, 5 V's, and 4 X's.