The Brussels choice (or Choix de Bruxelles) operation changes one number to another by taking a substring of the digits and either doubling it or (if the number is even) halving it. For example, starting with 9 and highlighting substrings, one can generate this sequence:
9, 18, 36, 312, 622, 644, 1288, 1488,...
Another possibility is
9, 18, 116, 232, 464, 924, 1844, 1888,...
Both of these excerpts have eight entries, but the second ends in a larger number than the first.
Write a function that takes an initial value and determines the largest number resulting after n steps. In the above examples, = 9 and . Return the number as a character string.

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Last Solution submitted on Dec 16, 2025

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