The leading digit can only be 1 or 2, and as when multiplied by 4 you get the

digits reversed it cannout be 1 (as then we would have an even number ending in 1),

so the number is of the form 2 . . . 8

Now the next most significant digit must be 0, 1 or 2 (as there is no carry when

multiplied by 4), and trial and error show that 21978 * 4 = 87912

RonL