Here is the full list of all 21 Happy Numbers achievements.
Meet Nika for the first time.
Meet Yona for the first time.
Meet Niall for the first time.
Meet Nona for the first time.
Meet Eli for the first time.
Meet Amery for the first time.
Passed 70 levels.
Passed 65 levels.
Passed 60 levels.
Passed 55 levels.
Passed 50 levels.
Passed 45 levels.
Passed 40 levels.
Passed 35 levels.
Passed 30 levels.
Passed 25 levels.
Meet Neron for the first time.
Meet Kasey for the first time.
Passed 20 levels.
Meet Kelly for the first time.
Meet Barnaby for the first time.