1引言印度境内某铁路沿线有一块里程指示牌,上面写着3025公里,由于受到龙卷风的袭击,路牌被拦腰折断,这个四位数字也被一分为二,一边为30,一边为25.有一天数学家喀普利卡(Kaprekar)偶然路经该地,看到这幕景象,突然心中一亮,他自言自语地说道:“这个数好奇怪呀:30+25=55,而552=3 1 INTRODUCTION There is a milesage sign along a railway in India, which reads 3025 kilometers. The street sign was broken due to a tornado. The four digits were also divided into two. One was 30, while the other was 25. One day the mathematician Kaprekar accidentally passed by the land, and when he saw the scene, he suddenly said to himself: “This is a strange number: 30+25=55, and 552 =3