20/n+2 €N => D20 = {2,4,5,10,20}
n+2€{2,4,5,10,20} | -2
n€{0,2,3,8,18}
A={0,2,3,8,18}
55/n+3€N => D55 = {11,55,5}
n+3€{11,55,5} |-3
n€{8,52,3}
B={8,52,3}
A intersectat cu B= {3;8}
Intersectia=Elementele care sunt si in A si in B (comune)
A\B={0;2;18}
Diferenta=Elementele care apartin lui A dar nu si lui B.