4位數字黑洞是什麼(10分)

An article in this publication demonstrated that the subtractive process applied to four-digit numbers would lead to a black hole of 6174. The four-digit subtractive process was used to reinforce subtraction skills for students in grades four through eight. Instead of providing the usual “boring” subtraction exercises

www.cs.southwestern.edu/txcmj/Black Holes-Loops.pdf
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