Answer:
4, 12, 36, 108
Step-by-step explanation:
a1: 4(3)^1-1 = 4(3)^0 = 4
a2: 4(3)^2-1 = 4(3)^1 = 12
a3: 4(3)^3-1 = 4(3)^2 = 36
a4: 4(3)^4-1 = 4(3)^3 = 108
