Question

aratati ca nr A=2021+2*(1+2+3+......+2020) ESTE PATRAT PERFECT

Answer 1

A=2021+2*(1+2+3+......+2020)=
=2021+2*2020*2021/2=
=2021+2020*3021=
=2021(1+2020)=
=2021*2021=
=2021²
deci patrat perfect

Answer 2

$\displaystyle 2021+2 \cdot (1+2+3+...+2020)=2021+2 \cdot \frac{2020(2020+1)}{2} = \\ \\ =2021+2 \cdot \frac{2020 \cdot 2021}{2} =2021+\not 2 \cdot \frac{4082420}{\not 2} =2021+4082420= \\ =2021(1+2020)=2021 \cdot 2021=2021^2-p.p$