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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 62 |
| 4 | 916 |
| 5 | 17644 |
| 6 | 419360 |
| 7 | 11859840 |
| 8 | 388965600 |
| 9 | 14514046560 |
| 10 | 607165485120 |
| 11 | 28143329181120 |
| 12 | 1431690475207680 |
| 13 | 79302863940387840 |
| 14 | 4751108622148907520 |
| 15 | 306118435580577146880 |
| 16 | 21107196651940518551040 |
| 17 | 1550773243761690603179520 |
| 18 | 120947288498720390755353600 |
[1,1,6,62,916,17644,419360,11859840,388965600, 14514046560,607165485120,28143329181120, 1431690475207680,79302863940387840, 4751108622148907520,306118435580577146880, 21107196651940518551040,1550773243761690603179520, 120947288498720390755353600] |