Sa se arate ca,oricare ar fi numarul natural n:

[tex]\it 25^{n+1}\cdot3^{2n+2}-5^{2n}\cdot9^{n+2}=25^n\cdot25\cdot9^n\cdot9-25^n\cdot9^n\cdot9=\\ \\ =25^n\cdot9^n(25\cdot9-9^2)=(25\cdot9)^n(225-81)=225^n\cdot144=\\ \\ =225^n\cdot6\cdot24\in M_{24}[/tex]