0
Oasis, 4 bytes (non-competing)
Probably my last language from the golfing family! Non-competing, since the language postdates the challenge.
Code:
²->2
Expanded version:
a(n) = ²->
a(0) = 2
Explanation:
² # Stack is empty, so calculate a(n - 1).
- # Subtract, arity 2, so use a(n - ...