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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 80 |
| 4 | 800 |
| 5 | 6248 |
| 6 | 43424 |
| 7 | 283880 |
| 8 | 1793600 |
| 9 | 11110088 |
| 10 | 68008544 |
| 11 | 413290280 |
| 12 | 2500208000 |
| 13 | 15081582728 |
| 14 | 90806120864 |
| 15 | 546088834280 |
| 16 | 3281497784000 |
| 17 | 19708713860168 |
| 18 | 118330793948384 |
| 19 | 710297609395880 |
| 20 | 4263033439001600 |
| 21 | 25583180948198408 |
| 22 | 153518974465539104 |
[0,4,80,800,6248,43424,283880,1793600,11110088, 68008544,413290280,2500208000,15081582728, 90806120864,546088834280,3281497784000, 19708713860168,118330793948384,710297609395880, 4263033439001600,25583180948198408, 153518974465539104] |