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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 9 |
| 2 | 36 |
| 3 | 240 |
| 4 | 1620 |
| 5 | 11808 |
| 6 | 88440 |
| 7 | 683280 |
| 8 | 5380020 |
| 9 | 43046640 |
| 10 | 348672528 |
| 11 | 2852823600 |
| 12 | 23535749880 |
| 13 | 195528140640 |
| 14 | 1634056262280 |
| 15 | 13726075468992 |
| 16 | 115813759112820 |
| 17 | 981010688215680 |
| 18 | 8338590828280440 |
| 19 | 71097458824894320 |
[1,9,36,240,1620,11808,88440,683280,5380020, 43046640,348672528,2852823600,23535749880, 195528140640,1634056262280,13726075468992, 115813759112820,981010688215680,8338590828280440, 71097458824894320] |