一位数4个:1,2,3,4;
两位数12个:12,13,14;21,23,24;31,32,34;41,42,43;
三位数24个:123,124,132,134,142,143;213,214,231,234,241,243,;312,314,321,324,341,342;412,413,421,423,431,432;
四位数24个:1234,1243,1324,1342,1423,1432;2134,2143,2314,2341,2413,2431;3124,3142,3214,3241,3412,3421;4123,4132,4213,4231,4312,4321;
因为4+12+24=40,所以第41个数是四位数中最小的那个,即1234.