... also, has there been any investigation as to why the digits need to be different? Clearly, this works for some numbers with repeating digits, eg

9871 - 1789 = 8082 -> since 9871 reaches 6174 so much 8082

thank you

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## why only different digits

... also, has there been any investigation as to why the digits need to be different? Clearly, this works for some numbers with repeating digits, eg

9871 - 1789 = 8082 -> since 9871 reaches 6174 so much 8082

thank you