Răspuns :
2006 + 2×(1+2+3+...+2005)=
=2006+2×2005×2006/2=
=2006+2005×2006=
=2006×(1+2005)=
=2006×2006=
=2006²
=2006+2×2005×2006/2=
=2006+2005×2006=
=2006×(1+2005)=
=2006×2006=
=2006²