Which of these is a linear non-homogeneous recurrence?
an=an−1+an−2a_n = a_{n-1} + a_{n-2}an=an−1+an−2
an=2an−1+na_n = 2a_{n-1} + nan=2an−1+n
an=an−12a_n = a_{n-1}^2an=an−12
an=n⋅an−1a_n = n \cdot a_{n-1}an=n⋅an−1