1. 4^3=16*4=64
5^3=25*5=125
7^3=49*7=343
2.U(5^7)=5, U(6^2005)=6, U(11^2004)=1
daca le adun obtin U(nr)=2 care nu este cifra unui patrat perfect
3. 24^2+25*x≤ 606
576+25*x≤606
25*x≤606-576
25*x≤30
x∈{0,1}
4. U (436^2004+4)=0 ⇒ nr se imparte exact la 10 ⇒ r=0
5. U (16^2006)=6
U(17^2007)=U(7^3)=3 (pt ca 2007:4=501 rest 3 )
U (18^2008)=U(8^4)=6 (pt ca 2008:4=502)
U(19^2009)=U(9^1)=9 pt ca 2009 e nr impar
U (20^2010)=0
daca le adun U(n)=U(6+3+6+9)=4
