The expressions that can represent the dimensions of the prim is (x), (3x+1) and (4x-1).
Natural number are basically " counting numbers ". They have no decimals, no fractions, and no negative numbers. It is debated whether 0 is included.
so ur natural numbers less then 3 are {1,2 }...not 100% sure if u include 0. I do not think u do.