(FRA1) Let a and b be two nonnegative integers. Denote by H(a,b) the set of numbers n of the form n=pa+qb, where p and q are positive integers. Determine H(a)=H(a,a). Prove that if a=b, it is enough to know all the sets H(a,b) for coprime numbers a,b in order to know all the sets H(a,b). Prove that in the case of coprime numbers a and b,H(a,b) contains all numbers greater than or equal to ω=(a−1)(b−1) and also 2ω numbers smaller than ω number theorycoprimeFrobeniusAdditive Number TheoryIMO ShortlistIMO Longlist