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Help with Lockdown decisions...

Arab Horse said:
Whatever number you choose it comes to 9; very clever.
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Yes, but sadly not my idea originally. Reasoning:

Choose n, calculate 3n, then 3n+3. Multiplying by 3 again gives 9n+9, ie a multiple of 9.
Summing the digits of any two-digit multiple of 9 always gives 9.
 
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