将所有满足各位数字恰好依次增大的四位数按从小到大的顺序排成一行：1234,1235…6789,则此数列中的第98个数是多少?

Question

将所有满足各位数字恰好依次增大的四位数按从小到大的顺序排成一行：1234,1235…6789,则此数列中的第98个数是多少?

Answer 1

1234,1235,1236,1237,1238,1239,1245,1246,1247,1248,1249,1256,1257,1258,1259,1267,1268,1269,1278,1279,1289;(21)
1345,1346,1347,1348,1349,1356,1357,1358,1359,1367,1368,1369,1378,1379,1389;(15)
1456,1457,1458,1459,1467,1468,1469,1478,1479,1489;(10)
1567,1568,1569,1578,1579,1589;(6)
1678,1679,1689; (3)
1789;(1)
2345,2346,2347,2348,2349,2356,2357,2358,2359,2367,2368,2369,2378,2379,2389;(15)
2456,2457,2458,2459,2467,2468,2469,2478,2479,2489;(10)
2567,2568,2569,2578,2579,2589;(6)
2678,2679,2689;(3)
2789;(1)
3456,3457,3458,3459,3467,3468,【3469】,3478,3479,3489;(10)
3567,3568,3569,3578,3579,3589;(6)
3678,3679,3689;(3)
3789;(1)
4567,4568,4569,4578,4579,4589;(6)
4678,4679,4689;(3)
4789;(1)
5678,5679,5689;(3)
5789;(1)
6789.(1)
所以第98个数字是3469.