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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 8 |
| 3 | 57 |
| 4 | 428 |
| 5 | 3510 |
| 6 | 31644 |
| 7 | 312984 |
| 8 | 3380544 |
| 9 | 39664080 |
| 10 | 502927200 |
| 11 | 6858181440 |
| 12 | 100135491840 |
| 13 | 1559197261440 |
| 14 | 25797280723200 |
| 15 | 452046655872000 |
| 16 | 8364495012249600 |
| 17 | 162994310248089600 |
| 18 | 3336683369519001600 |
| 19 | 71596721810396160000 |
| 20 | 1606993396943155200000 |
[1,8,57,428,3510,31644,312984,3380544,39664080, 502927200,6858181440,100135491840,1559197261440, 25797280723200,452046655872000,8364495012249600, 162994310248089600,3336683369519001600, 71596721810396160000,1606993396943155200000] |