  In Martin Gardner's October, 1976 Mathematical Games column in Scientific
American, he posed the following problem: "What is the smallest number of
[queens] you can put on a board of side n such that no [queen] can be added
without creating three in a row, a column, or a diagonal?" We use the
Combinatorial Nullstellensatz to prove that this number is at least n, except
in the case when n is congruent to 3 modulo 4, in which case one less may
suffice. A second, more elementary proof is also offered in the case that n is
even.
