Which recurrence is homogeneous?
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−1+2na_n = a_{n-1} + 2^nan=an−1+2n
an=an−1+na_n = a_{n-1} + nan=an−1+n