“Lucky Number Seven”

A natural number a is called a “lucky number” if the sum of its digits is seven. Arrange all “lucky number” in an ascending order, and we get a sequence $a_{1} , a_{2} , …..$. If $ a_{n}$=2005, then $a_{5n}$=

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.