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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 31 |
| 4 | 360 |
| 5 | 5601 |
| 6 | 109568 |
| 7 | 2586151 |
| 8 | 71555200 |
| 9 | 2271961825 |
| 10 | 81441188352 |
| 11 | 3253620672303 |
| 12 | 143361363439616 |
| 13 | 6907049546879041 |
| 14 | 361245668908466176 |
| 15 | 20383791705206338807 |
| 16 | 1234336634416972726272 |
| 17 | 79843983527411321710401 |
| 18 | 5494767253686351671459840 |
| 19 | 400863405346004202504321343 |
[1,1,4,31,360,5601,109568,2586151,71555200, 2271961825,81441188352,3253620672303, 143361363439616,6907049546879041, 361245668908466176,20383791705206338807, 1234336634416972726272,79843983527411321710401, 5494767253686351671459840, 400863405346004202504321343] |