goi so can tim la ab
khi viet so do vao giua 2 chu so cua no dc aabb
ta co abx66=aabb
=>(10a+b)x66=1100a+11b
cung bot 660a+11bcua 2 ve dc 55b=440a
,<=>b =8a
vi 8a la so chan nen ba so chan => b la cac chu so 2,4,6,8
vs b=0 thi a=0 loai vi a ko =0
vs b= 2,4,6 thi a ko ton tai loai vi a la chu so
voi b = 8 thi a=1
vay so can tim la 18