Numbers
The number 2 in braille
2 is the number sign followed by the letter b — dots 1 and 2.
Number sign + b
Dots 3-4-5-6, then dots 1-2
Why it uses a letter
The first ten letters of the alphabet double as the ten digits. b is letter 2 of the alphabet, so after a number sign it reads as 2. Without the number sign the same cell is simply the letter b — see B in braille.
2 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.
2
12
200