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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 4 |
| 6 | 36 |
| 7 | 225 |
| 8 | 7840 |
| 9 | 313600 |
| 10 | 45302400 |
| 11 | 8930250000 |
| 12 | 8373836401920 |
| 13 | 9001015156742400 |
| 14 | 41813367543204433176 |
| 15 | 325385777102562972821025 |
| 16 | 8270190445766978650521600000 |
| 17 | 377177413291384771899817984000000 |
| 18 | 62187743659065606074696974956949929984 |
[1,1,1,2,4,36,225,7840,313600,45302400,8930250000, 8373836401920,9001015156742400, 41813367543204433176,325385777102562972821025, 8270190445766978650521600000, 377177413291384771899817984000000, 62187743659065606074696974956949929984] |