[tex]\it a=4^{20}\cdot3+2^{40}\cdot5+2^{40}=(2^2)^{20}\cdot3+2^{40}\cdot5+2^{40}=\\ \\ =2^{40}\cdot3+2^{40}\cdot5+2^{40}=2^{40}(3+5+1)=2^{40}\cdot9=(2^{20})^2\cdot3^2=[2^{20}\cdot3]^2[/tex]
