Numbers
The number 9 in braille
9 is the number sign followed by the letter i — dots 2 and 4.
Number sign + i
Dots 3-4-5-6, then dots 2-4
Why it uses a letter
The first ten letters of the alphabet double as the ten digits. i is letter 9 of the alphabet, so after a number sign it reads as 9. Without the number sign the same cell is simply the letter i — see I in braille.
9 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.
9
19
900