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