The sum of the cubes of its own digits is equal to an Armstrong number, also known as a narcissistic number. In number theory, a narcissistic number is a number that is the sum of its own digits each raised to the power of the number of digits in a given number base b.

```
lower = 100
upper = 400
for num in range(lower, upper + 1):
order = len(str(num))
sum = 0
temp = num
while temp > 0:
digit = temp % 10
sum += digit ** order
temp //= 10
if num == sum:
print(num)
```

Output:

153

370

371

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