Mark changed a new number, and he found that there are three characteristics that make the new phone number easy to remember: first, the original number and the new number are both four digits; second, the new number is exactly four times the original number; , the original number written backwards from the back happens to be the new number. Therefore, he will remember the new number without much effort, so what is the new number.
马克又换了新号码，他发现，有三个特点使新的电话号码很好记：首先，原来的号码和新的号码都是四个数字；其次，新号码正好是原来号码的4倍；再次，原来的号码从后面倒着写正好是新的号码．所以，他不费劲就会记住新号码，那么，新号码是多少．
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