Explain this:

but first, notice this: if from 153 you take every digits (1,5,3) compute the cube of those digits and add them, you get back 153

(1^3 + 5^3 + 3^3) = 1 +125 + 27 = 153

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Then pick any 3 digits number that can be divided by 3, any one

and do the same thing, then with the answer found, just repeat the same thing again, and again. You will always end up with 153

Example

take 342

3^3 + 4^3 + 2^3 = 99

9^3 + 9^3 =1458

1^3 + 4^3 +5^3 + 8^3 = 702

7^3 + 2^3 = 351

3^3 + 5^3 + 1^3 = 153

and other examples

666 gives you the sequence 648, 792, 1080, 513, 153

261 gives the sequence 225, 141, 66, 432, 99, 1458, 702, 351, 153

369 gives the sequence 972, 1080, 513, 153

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