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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 28 |
| 4 | 272 |
| 5 | 3369 |
| 6 | 50816 |
| 7 | 903856 |
| 8 | 18522624 |
| 9 | 429746905 |
| 10 | 11135257600 |
| 11 | 318719062236 |
| 12 | 9987013488640 |
| 13 | 340037795872369 |
| 14 | 12500401969233920 |
| 15 | 493467700789897408 |
| 16 | 20819865970795610112 |
| 17 | 934939160745193002321 |
| 18 | 44523294861684890664960 |
[1,1,4,28,272,3369,50816,903856,18522624, 429746905,11135257600,318719062236,9987013488640, 340037795872369,12500401969233920, 493467700789897408,20819865970795610112, 934939160745193002321,44523294861684890664960] |