The last upside-down year was 1961 - that is, you can turn 1961 upside down without changing its value.
When will the next upside-down year occur?

Solution to the Problem:

6009

However, James Alarie and Chad Fore both sent in solutions of 2002 which work on many calculators!
2002 would be the first year after 1961 that works, so the next upside year would be 2112, which was sent in by James Alarie and Alp Aribal.

Correctly solved by:

1. Kayla Burch Mountain View High School,
Mountain View, Wyoming
2. James Alarie Flint, Michigan
3. Steven Burak Drexel University,
Philadelphia, Pennsylvania
4. John Funk Ventura, California
5. Chad Fore Gate City, Virginia
6. Trey Briggs Mountain View High School,
Mountain View, Wyoming
7. Halee Salsbury Mountain View High School,
Mountain View, Wyoming
8. Kalvin Hereford Mountain View High School,
Mountain View, Wyoming
9. Brandon Preston Mountain View High School,
Mountain View, Wyoming
10. Tyler Cantrell Mountain View High School,
Mountain View, Wyoming
11. Mount Vernon Math Club Mount Vernon, Ohio
12. Peyton Madsen Mountain View High School,
Mountain View, Wyoming
12. Levi Harmon Mountain View High School,
Mountain View, Wyoming
13. Alp Aribal Istanbul, Turkey