------
## 最终结论
```python
def is_num_keith(n):
    digits = [int(d) for d in str(n)]
    seq = digits.copy()
    
    while True:
        next_num = sum(seq)
        if next_num == n:
            return True
        elif next_num > n:
            return False
        seq.append(next_num)
        seq.pop(0)

# Test cases
assert is_num_keith(14) == True
assert is_num_keith(12) == False
assert is_num_keith(197) == True
```