Răspuns :
x = 1004 + 2 + 4 + .. + 2006
x = 1004 + 2·(1 + 2 + .. + 1003)
x = 1004 + 2·1003·1004 : 2
x = 1004·(1 + 1003)
x = 1004·1004
x = 1004²
x = 1004+2(1+2+3+...+1003) = 1004+(2x1003x1004)/2 = 1004+1003x1004 =
= 1004x(1+1003) = 1004x1004 = 1004² ⇒ patrat perfect
