As we ease into 2021, here are 21 fun facts related to the number 21. 1 21 in Roman numerals is XXI. 2 21 is a triangle number – it is the sum of the first six whole numbers (1+2+3+4+5+6=21).

Super Bowl week is back, which means Roman numerals are once again at the forefront of the public consciousness. As one of the only institutions that still uses Roman numerals, the NFL's choice ...