Finding all paths down stairs?

Question

I was given the following problem in an interview:

Given a staircase with N steps, you can go up with 1 or 2 steps each time. Output all possible way

Answer 1

may be I am wrong.. but it should be :

S(1) =0
S(2) =1

Here We are considering permutations so in that way

S(3) =3
S(4) =7