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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 9 |
| 3 | 80 |
| 4 | 654 |
| 5 | 6264 |
| 6 | 59760 |
| 7 | 665160 |
| 8 | 7565040 |
| 9 | 96929280 |
| 10 | 1286046720 |
| 11 | 18976083840 |
| 12 | 286363123200 |
| 13 | 4775047200000 |
| 14 | 81792956044800 |
| 15 | 1515077749785600 |
| 16 | 28898470215014400 |
| 17 | 594066352700620800 |
| 18 | 12467555729620992000 |
| 19 | 280797084422959104000 |
| 20 | 6460327992512249856000 |
| 21 | 157769680941941612544000 |
[1,9,80,654,6264,59760,665160,7565040,96929280, 1286046720,18976083840,286363123200,4775047200000, 81792956044800,1515077749785600,28898470215014400, 594066352700620800,12467555729620992000, 280797084422959104000,6460327992512249856000, 157769680941941612544000] |