Răspuns :
Răspuns:
S= 1(1+2+3+...+18)= 3×(18(18+1))/2=3×9×19=513 care clar nu este p.p.
[tex]\it 3+6+9+12+\ ...\ +54 =3\cdot(1+2+3+4+\ ...\ +18)=3\cdot\dfrac{18\cdot19}{2}=\\ \\ =3\cdot9\cdot19= 513\\ \\ 22^2<513<23^2 \Rightarrow\ 513\ nu\ este\ p\breve{a}trat\ perfect[/tex]