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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 5 |
| 3 | 90 |
| 4 | 2210 |
| 5 | 67800 |
| 6 | 2484750 |
| 7 | 105772800 |
| 8 | 5128126100 |
| 9 | 278995708800 |
| 10 | 16834806218750 |
| 11 | 1115967716160000 |
| 12 | 80627283335101500 |
| 13 | 6306411043525632000 |
| 14 | 530946503562997987500 |
| 15 | 47876129916092928000000 |
| 16 | 4603521212261405490225000 |
| 17 | 470209485165582143631360000 |
| 18 | 50843713447609660550744718750 |
[1,5,90,2210,67800,2484750,105772800,5128126100, 278995708800,16834806218750,1115967716160000, 80627283335101500,6306411043525632000, 530946503562997987500,47876129916092928000000, 4603521212261405490225000, 470209485165582143631360000, 50843713447609660550744718750] |