Numbers
The number 1 in braille
1 is the number sign followed by the letter a — dot 1.
Number sign + a
Dots 3-4-5-6, then dots 1
Why it uses a letter
The first ten letters of the alphabet double as the ten digits. a is letter 1 of the alphabet, so after a number sign it reads as 1. Without the number sign the same cell is simply the letter a — see A in braille.
1 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.
1
11
100