Here is the full list of all 12 Beltex achievements.
Reach maximum level on all upgrades
Reach level 15 without building multipliers or substractors
Reach level 12 without building bridges
Deliver 18 numbers per second
Deliver 36 numbers per second
Deliver 54 numbers per second
Deliver 10,000 numbers
Deliver 100,000 numbers
Deliver 1,000,000 numbers
Reach level 10
Reach level 20
Reach level 30