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假設有一個四位數abcd,它可以表示成以下形式:abcd=1000a+100b+10c+d=999a+99b+9c+a+b+c+d=9×(111a+11b+c)+a+b+c+d可以看出,9×(111a+11b+c)必定能被3整除,所以判斷abcd能否被3整除,就看a+b+c+d能被3整除,也就是看…
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