For the Frobenius Coin Problem, where $n = 3$
http://en.wikipedia.org/wiki/Coin_problem
Does anyone know a proof for Davidson's formula? The one that states that the lower bound for the Frobenius number is $$\sqrt{3 a_1 a_2 a_3}-a_1-a_2-a_3$$
Also, any links on proofs and duscussions on the other lower bound formulas like Selmer and Beyer's and Rodseth's?