a) 2010² -2010- 2009 = 2010 (2010 -1) -2009 = 2010·2009 -2009 = 2009 (2010-1) =2009·2009 = 2009² =p.p.
b) 2·5·6/2 + 6 = 36 =6² p.p.
c) 10 + 20 +30 + ........+190 =10 (1+2+3+.......+19) = 10·19·20/2 =10² ·19 ≠p.p.
2) a) 2^1981 = 2^1980 ·2 =( 2^990)² ·2 ≠ p.p.
b) 3^1883 = 3^1882 ·3= (3^941)² ·3 ≠ p.p.
c) 5^17 (517 +1) = 5^17 ·518 = 5^16 ·2590≠p.p. (5^16=p.p. ; 2590 ≠p.p.)
d) Uc(5^6 +2)= 7 nu exista p.p. cu Uc=7