We divide $999\times 999$ square into the angles with $3$ cells. Prove, that number of ways is divided by $2^7$.( Angle is a figure, that we can get if we remove one cell from $2 \times 2$ square).
Source: Moscow Olympiad 2018, Grade 10, P6
Tags: combinatorics
We divide $999\times 999$ square into the angles with $3$ cells. Prove, that number of ways is divided by $2^7$.( Angle is a figure, that we can get if we remove one cell from $2 \times 2$ square).