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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 9 |
| 3 | 9 |
| 4 | 234 |
| 5 | 558 |
| 6 | 12024 |
| 7 | 47736 |
| 8 | 1021680 |
| 9 | 5795280 |
| 10 | 129418560 |
| 11 | 963938880 |
| 12 | 22835675520 |
| 13 | 211767696000 |
| 14 | 5349794688000 |
| 15 | 59562324864000 |
| 16 | 1605652989696000 |
| 17 | 20903846245632000 |
| 18 | 600544575525888000 |
| 19 | 8962083073778688000 |
| 20 | 273802240880695296000 |
| 21 | 4611450448589580288000 |
[0,9,9,234,558,12024,47736,1021680,5795280, 129418560,963938880,22835675520,211767696000, 5349794688000,59562324864000,1605652989696000, 20903846245632000,600544575525888000, 8962083073778688000,273802240880695296000, 4611450448589580288000] |