For example, 42 = 21 + 21, so it is not a candidate. 22 is a candidate because no pair of 9, 15, or 21 can equal 22.
As with many of Mr. Tanton's puzzles, there's a way to know that you are absolutely correct. Can you find the number and the explanation?
What is the largest even integer that cannot be written as the sum of two odd composite numbers?
— James Tanton (@jamestanton) May 25, 2014