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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 9 |
| 2 | 18 |
| 3 | 54 |
| 4 | 216 |
| 5 | 1080 |
| 6 | 6480 |
| 7 | 45360 |
| 8 | 362880 |
| 9 | 3265920 |
| 10 | 32659200 |
| 11 | 359251200 |
| 12 | 4311014400 |
| 13 | 56043187200 |
| 14 | 784604620800 |
| 15 | 11769069312000 |
| 16 | 188305108992000 |
| 17 | 3201186852864000 |
| 18 | 57621363351552000 |
| 19 | 1094805903679488000 |
| 20 | 21896118073589760000 |
| 21 | 459818479545384960000 |
[0,9,18,54,216,1080,6480,45360,362880,3265920, 32659200,359251200,4311014400,56043187200, 784604620800,11769069312000,188305108992000, 3201186852864000,57621363351552000, 1094805903679488000,21896118073589760000, 459818479545384960000] |