(base 32)810 % 31 <==> (base 10) ( 8 * (32^2) + 1 * (32^1) + 0 * (32^0) ) % 31
<==> (base 10) ( 8 * ( (31+ 1)^2) + 1 * ( (31+ 1)^1) + 0 * 1 ) % 31
<==> (base 10) ( 8 * ( 31^2 + 2*31 + 1) + 1 * ( 31+ 1) + 0 ) % 31
<==> (base 10) ( 8 * 1 + 1 * 1 + 0 ) % 31 = (8+1+0) % 31,所以(base 32)810 % 31 = (base 10) 9 % 31 = 9