Here is the full list of all 14 Three Digits achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Complete the Full #1 pack.
Complete the Awkward Range pack.
Complete the Prime Time pack.
Complete the Beginner pack.
Complete the Halfway pack.
Complete the Seven Fifty pack.
Complete the Full #2 pack.
Complete the Awkward Range Reversed pack.
Complete the We Aren't Divisible By 2 pack.
Complete the Full #3 pack.
Complete the Threes pack.
Complete the Pure Three Digits pack.
Complete the Full #4 pack.
Complete the Last Three pack.