a) U(28^199) =U( 8^199) = U( (8^4)^49 *8^3) =U( 6^49 * 2)=U(6*2)=2
b)10*n+2
U(10*n+2 )=U(0+2)=2
c) U(10n+7)=U(0+7)=7
d) 2+4+...+2n =2*(1+2+...+n) =2*n*(n+1)/2 =n*(n+1)
e)daca n=nr par=> U(5*n+2)=U(0+2)=2
daca n=nr impar => U(5*n+2)=U(5+2) =7
UN nr POATE fi p.p. daca are ultima cifra 1,4,5,6,9
U ( ) = ultima cifra
* = produs
p.p =patrat perfect
