Whether you're age 8 or age CVIII, Wolfram|Alpha's algorithmic understanding of historical number systems allows you to compute like the ancients. Use Wolfram|Alpha to convert commonly seen Roman numerals to modern decimal numbers or to translate decimal numbers to their Mayan, Greek or Babylonian equivalents.
Convert decimal numbers to and from Roman numerals.
Explore the representation of decimal numbers in ancient Mayan numerals.
Explore the representation of decimal numbers in ancient Greek numerals.
Can't count in cuneiform? Convert to and from Babylonian numerals.