^=la puterea
2^(n+1)-2^n=2^n(2^1-2^0)=2^n divizibil cu 2^n
3^(n+1)+3^n=3^n(3^1 +3^0)=3^n * (3+1)=3^n * 4 deci divizibil cu 4
5^(n+2)-5^(n+1)+5^n=5^n(5^2-5^1+5^0)=5^n(25-5+1)=5^n * 21 deci divizibil cu 21
8^(3n+1)+4^(3n+1)-11*64^n=2^3*(3n+1)+2^2*(3n+1)-11*2^6n=
=2^(9n+3)+2^(6n+2)-11*2^6n=2^6n * [2^(3n+3)+2^2-11] divizibil cu 2^6n