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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 18 |
| 3 | 246 |
| 4 | 3016 |
| 5 | 34920 |
| 6 | 390480 |
| 7 | 4266640 |
| 8 | 45866880 |
| 9 | 487198080 |
| 10 | 5128019200 |
| 11 | 53591788800 |
| 12 | 556898534400 |
| 13 | 5760319052800 |
| 14 | 59355533260800 |
| 15 | 609667001088000 |
| 16 | 6245327982592000 |
| 17 | 63829424295936000 |
| 18 | 651070362673152000 |
| 19 | 6629663109210112000 |
| 20 | 67406737815797760000 |
[1,18,246,3016,34920,390480,4266640,45866880, 487198080,5128019200,53591788800,556898534400, 5760319052800,59355533260800,609667001088000, 6245327982592000,63829424295936000, 651070362673152000,6629663109210112000, 67406737815797760000] |