Define the recurrence an=an−1⋅an−2a_n = a_{n-1} \cdot a_{n-2}an=an−1⋅an−2 with a0=2a_0 = 2a0=2 and a1=3a_1 = 3a1=3 (multiplicative, not additive). What is a4a_4a4?
18
108
648
1296