Numbers
The number 4 in braille
4 is the number sign followed by the letter d — dots 1, 4 and 5.
Number sign + d
Dots 3-4-5-6, then dots 1-4-5
Why it uses a letter
The first ten letters of the alphabet double as the ten digits. d is letter 4 of the alphabet, so after a number sign it reads as 4. Without the number sign the same cell is simply the letter d — see D in braille.
4 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.
4
14
400