March 30–April 5, 2010
Make a sequence a1, a2, a3, ... as follows: Pick any natural number for a1, and let an+1 = an + d, where d is some nonzero digit of an. Prove that this sequence must contain an even number.
List of solvers
Peiyush Jain, Lloyd Sakazaki, Lincoln Atkinson, Joshua Lim, Jens Malmquist, Chaitanya Rachabattuni, Steve Wilmarth, Rajneesh Hegde, Congpa You, Gary Mager, Jason Shaw, Mike Goodman.
Lincoln Atkinson wins the prize!