定义:对于一个各数位上的数字都不为 0 且互不相等的四位正整数, 若千位上的数字与个位上的数字之差等于十位上的数字与百位上的数字之和, 则称这样的四位数为 “匹配数”、将 “匹配数”
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi+mathvariant%3D%22normal%22%3Em%3C%2Fmi%3E%3C%2Fmath%3E)
的千位、百位所组成的两位数与十位, 个位所组成的两位数对调, 得到一个新的四位数
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%3En%3C%2Fmi%3E%3C%2Fmath%3E)
, 记
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%3EF%3C%2Fmi%3E%3Cmo%3E%28%3C%2Fmo%3E%3Cmi%3Em%3C%2Fmi%3E%3Cmo%3E%29%3C%2Fmo%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmo%3E%28%3C%2Fmo%3E%3Cmi%3Em%3C%2Fmi%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmi%3En%3C%2Fmi%3E%3Cmo%3E%29%3C%2Fmo%3E%3Cmo%3E%2F%3C%2Fmo%3E%3Cmn%3E101%3C%2Fmn%3E%3C%2Fmath%3E)
, 例如, 对于 6231 , 各位数上的数字都不为 0 且互不相等, 又因为
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmn%3E6%3C%2Fmn%3E%3Cmo%3E%E2%88%92%3C%2Fmo%3E%3Cmn%3E1%3C%2Fmn%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmn%3E2%3C%2Fmn%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmn%3E3%3C%2Fmn%3E%3C%2Fmath%3E)
, 所以 6231 是 “匹配数”。
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmi%3EF%3C%2Fmi%3E%3Cmo%3E%28%3C%2Fmo%3E%3Cmn%3E6231%3C%2Fmn%3E%3Cmo%3E%29%3C%2Fmo%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmo%3E%28%3C%2Fmo%3E%3Cmn%3E6231%3C%2Fmn%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmn%3E3162%3C%2Fmn%3E%3Cmo%3E%29%3C%2Fmo%3E%3Cmo%3E%2F%3C%2Fmo%3E%3Cmn%3E101%3C%2Fmn%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmn%3E93%3C%2Fmn%3E%3C%2Fmath%3E)
, 再如. 对于 9125 , 各位数上的数字都不为 0 且互不相等, 但因为
![](http://math.21cnjy.com/mml2svg?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmn%3E9%3C%2Fmn%3E%3Cmo%3E%E2%88%92%3C%2Fmo%3E%3Cmn%3E5%3C%2Fmn%3E%3Cmo%3E%E2%89%A0%3C%2Fmo%3E%3Cmn%3E1%3C%2Fmn%3E%3Cmo%3E%2B%3C%2Fmo%3E%3Cmn%3E2%3C%2Fmn%3E%3C%2Fmath%3E)
, 所以 9125 不是 “匹配数”