S (n+1)-3sn+2s (n-1) = 0 (n ≥ 2 and n ∈ n),

The deformed s (n+1)-sn = 2 [sn-s (n-1)] means a(n+ 1)=2an.

While a2/a 1= 1 is not equal to 2.

So {an} is not a geometric series.

(But after removing the first term, it is a geometric series.)