Numbers
The number 3 in braille
3 is the number sign followed by the letter c — dots 1 and 4.
Number sign + c
Dots 3-4-5-6, then dots 1-4
Why it uses a letter
The first ten letters of the alphabet double as the ten digits. c is letter 3 of the alphabet, so after a number sign it reads as 3. Without the number sign the same cell is simply the letter c — see C in braille.
3 inside larger numbers
A number sign covers the whole run of digits that follows it, so these examples each use one indicator regardless of length.
3
13
300