n = 105 + 2 ( 1 + 2 + 3 + 4 + .......+ 104 )
n = 105 + 2 × ( 104 × 105 ) / 2 → aplic formla sumei lui Gauss
1 + 2 + 3 + ......+ 104 = 104 ( termeni ) x ( 1 + 104 ) / 2 = 104 × 105 / 2
→ 2 / 2 = 1
n = 105 + 104 × 105
n = 105 ( 1 + 104 )
n = 105 × 105
n = 105²→ patrat perfect