Răspuns :
1+2+..+2000=2000*(1+2000/2)=2000* 2001/2=2001000
N=2001+2*2001000=2001+4002000=4004001=2001 este patrat perfect
proba: 2001*2001=4004001
N=2001+2*2001000=2001+4002000=4004001=2001 este patrat perfect
proba: 2001*2001=4004001
[tex]N=2001+\not2\cdot(\frac{2000\cdot2001}{\not2})=2001+2000\cdot2001=\\
=2001(1+2000)=2001^2[/tex]