x*b^2 + y*b + z = 1987
x+y+z = 25
x*(b+1)*(b-1) + y(b-1) = 1962 = 2 * 9 * 109
(x*(b+1) + y)*(b-1) = 2 * 9 * 109
显然100> b > 10,所以 b-1 = 18 => b=19
1987 = 104 * 19 + 11 = (5*19 + 9)*19 + 11
=> x=5,y=9,z=11(可用"B"表示,"A"表示10...),b=19