(2 ^ (N - 1)) grains of rice on the N'th square. That means (2 ^ N) - 1 cumulative grains of rice on the N first squares. So 63 total grains of rice on the fi

(2 ^ (N - 1)) grains of rice on the N'th square. That means (2 ^ N) - 1 cumulative grains of rice on the N first squares. So 63 total grains of rice on the first 6 squares is correct.