Ne folosim de suma lui Gauss
1+2+3+...+n=n(n+1):2
a) 1+2+3+... +500 + 251x501= 500(500+1):2+125751=500x501:2+125751=
250500:2+125751=125250+125751=251001=501²
b) 1+2+3+...+2021+1010+2021=2021(2021+1):2+3031=2021x2022:2+3031=
2021x1011+3031=2043231+3031=2046262
2046262 nu este patrat perfect, mai verifica odata daca enuntul este bun