Here is the full list of all 13 Two Digits achievements. It takes around 5-6 hours to unlock all of the achievements on Windows.
Complete the Ultimate Level.
Complete the Three pack.
Complete the Full #3 pack.
Complete the Two Digits Only pack.
Complete the Odd pack.
Complete the Full #2 pack.
Complete the Ninety Percent pack.
Complete the Full #1 pack.
Complete the Primary pack.
Use all the 9 numbers to complete a level.
Complete the Three Quarter pack.
Complete the First Steps pack.
Complete the Moving Up pack.