Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
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a)Ta thấy 11..11 có tổng các chữ số là n.Ta có:
2n+11...1=2n+n=3n chia hết cho 3