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March 30–April 5, 2010

Problem

Make a sequence a₁, a₂, a₃, ... as follows: Pick any natural number for a₁, and let a_n+1 = a_n + d, where d is some nonzero digit of a_n. Prove that this sequence must contain an even number.

Solution

here.

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!