Generate the Abacaba sequence

Pyth, 11 bytes

u++GHG<GhQk

Simple reduction.

Python, 44 bytes

f=lambda n:"a"[n:]or f(n-1)+chr(97+n)+f(n-1)

Looks suspiciously might-be-golfable.

Haskell, 39 37 bytes

a 0="a"
a n=a(n-1)++['a'..]!!n:a(n-1)

Usage example: a 3 -> "abacabadabacaba".

Edit: @Angs found two bytes to save. Thanks!