We recursively divide n by 3. If we reach 1, it's a power of three. If we reach a number not divisible by 3 (and not 1), it's not.

1. If n <= 0, return False.
2. If n == 1, return True.
3. If n % 3 != 0, return False.
4. Recursive step: Return is_power_of_three(n // 3).

• Time Complexity: O(log3 N).
• Space Complexity: O(log3 N).

def is_power_of_three(n):
    if n <= 0: return False
    if n == 1: return True
    return n % 3 == 0 and is_power_of_three(n // 3)