Question

从4到9一共有多少个四位数字

能把数字都列出来吗？

Answer 1

从4,5,6,7,8,9共6个数字中每次取4个数字组成一个四位数，总共能组成多少个四位数，也就是求从六个元素中取四个元素的排列=6!/(6-4)!=360。用字典法可举出：
4567,4568,4569,4576,4578,4579,4586,4587,4589,4596,4597,4598;
4657,4658,4659,4675,4678,4679,4685,4687,4689,4695,4697,4698;
4756,4758,4759,4765,4768,4769,4785,4786,4789,4795,4796,4798;
4856,4857,4859,4865,4867,4869,4875,4876,4879,4895,4896,4897;
4956,4957,4958.4965,4967,4968,4975,4976,4978,4985,4986,4987;
5467,5468,5469,5476,5478,5479,5486,5487,5489,5496,5497,5498;
5647,5648,5649,5674,5678,5679,5684.5687,5689,5694.5697.5698;
5746,5748,5749,5764,5768,5769,5784,5786,5789,5794,5796.5798;
5846,5847,5849,5864,5867,5869,5874,5876,5879,5894,5896,5897;
5946,5947,5948,5964,5967,5968,5974,5976,5978,5984,5986,5987;
6457,6458,6459,6475,6478,6479,6485,6487,6489,6495,6497,6498;
6547,6548,6549,6574,6578,6579,6584,6587,6589,6594,6597,6598;
6745,6748,6549,6754,6758,6759,6784,6785,6789,6794,6795,6798;
6845,6847,6849,6854,6857,6859,6874,6875,6879,6894,6895,6897;
6945,6947,6948,6954,6957,6958,6974,6975,6979,6984,6985,6987;
7456,7458,7459,7465,7468,7469,7485,7486,7489,7495,7496,7498;
7546,7548,7549,7564,7568,7569,7584,7586,7589,7594,7596,7598;
7645,7648,7649,7654,7658,7659,7684,7685,7689,7694,7695,7698;
7845,7846,7849,7854,7856,7859,7864,7865,7869,7894,7895,7896;
7945,7946,7948,7954,7956,7958,7964,7965,7968,7984,7985,7986;
8456,8457,8459.8465,8467,8469,8475,8476,8479,8495,8496,8497;
8546,8547,8549,8564,8567,8569,8574,8576,8579,8594,8596,8597;
8645,8647,8649,8654,8657,8659,8674,8675,8679,8694,8695,8687;
8745,8746,8749,8754,8756,8759,8764,8765,8769,8794,8795,8796;
8945,8946,8947,8954,8956,8957,8964,8965,8967,8974,8975,8976;
9456,8457,9458,9465,9467,9468,9475,9476,9578,9485,9486,9487;
9546,9547,9548,9564.9567,9568,9574,9576,9578,9584,9586,9587;
9645,9647,9648.9654,9657,9658,9674,9675,9678,9684,9685,9687;
9745,9746,9748,9754,9756,9758.9764,9765,9768,9784,9785,9786;
9845,9846,9847,9854,9856,9857,9864,9865,9867,9874,9875,9876.

Answer 2

那不都个位的嘛