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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 6 |
| 3 | 78 |
| 4 | 588 |
| 5 | 6804 |
| 6 | 62496 |
| 7 | 753984 |
| 8 | 8273664 |
| 9 | 109118016 |
| 10 | 1408700160 |
| 11 | 20697223680 |
| 12 | 309818234880 |
| 13 | 5100265336320 |
| 14 | 87215844925440 |
| 15 | 1605019401216000 |
| 16 | 30898776106598400 |
| 17 | 631358784683827200 |
| 18 | 13503510009903513600 |
| 19 | 303781522335363072000 |
| 20 | 7137966147222822912000 |
[1,6,78,588,6804,62496,753984,8273664,109118016, 1408700160,20697223680,309818234880,5100265336320, 87215844925440,1605019401216000,30898776106598400, 631358784683827200,13503510009903513600, 303781522335363072000,7137966147222822912000] |