The quantity of rice on the first square is 20 rather than 2, so the quantity on the last square is 263

The quantity of rice on the first square is 1. The quantity of rice on the 2nd square is therefore 2 - leaving 62 squares of the total 64. Therefore 2 to the power of 62 - or have I missed something?

1 to the power of 64 is 1.