Numbers
The number 7 in braille
7 is the number sign followed by the letter g — dots 1, 2, 4 and 5.
Number sign + g
Dots 3-4-5-6, then dots 1-2-4-5
Why it uses a letter
The first ten letters of the alphabet double as the ten digits. g is letter 7 of the alphabet, so after a number sign it reads as 7. Without the number sign the same cell is simply the letter g — see G in braille.
7 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.
7
17
700