A regular cubical dice has 21 dots. 1+2+3+4+5+6=21
3 Prime Colors
It will be 1 + 2 + 3 + 4 + 5 + 6 = 21 dots
"Three Wheels on a Tricycle".
There are 21 spots on a dice.1+2+3+4+5+6 = 21 dots on a die.
(6+5+4+3+2+1) x 4 = 84
3 Little Birds by Bob Marley and the Wailers
3 piece suite (3 p's sweet)
2/9!
There are many different shapes and sizes of dice. The typical die that you find in most board games has 6 sides and 6 numbers. There are also 6-sided dice that are made with only 3 options though, and there are 20 and 30 sided dice out there as well. There are also 4 sided dice, 8 sided, 10 sided, and 12 sided that are quite common. They have other (even odd) numbered dice, and other types of dice with math symbols or pictures on them instead of numbers. Or letter dice for word games sometimes.
Feet first!
They don't HAVE to - it's just the way dice have always been marked. You could have a dice that has 6 & 5, 3 & 4 and 1 & 2 on opposite sides - it would still be a dice but wouldn't follow the 'opposites total 7' rule.