Multi-tap or multi-press is the name given to the historic technique of writing SMS on the first mobile phones with a keyboard of 10-12 numeric keys.
For example, to type LOL you need to press 5 three times, 6 three times and 5 three times again.
Your task is to write a function that takes a string as input and returns the repeated digits associated with each character according to the multi-tap system.

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