Which of the following is NOT a linear recurrence relation?
an=5an−1−4a_n = 5a_{n-1} - 4an=5an−1−4
an=an−1+2an−2a_n = a_{n-1} + 2a_{n-2}an=an−1+2an−2
an=an−12+an−2a_n = a_{n-1}^2 + a_{n-2}an=an−12+an−2
an=0.5an−1+3a_n = 0.5a_{n-1} + 3an=0.5an−1+3