There are 3 auspicious numbers: 888, 518, and 666. Divide them by the same natural number, and the remainders are a, a+7, and a+10. Find this natural number.
有3个吉利数：888，518，666，用它们分别除以同一个自然数，所得余数依次为a，a+7，a+10，求这个自然数．
<result>29</result>