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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 41 |
| 3 | 602 |
| 4 | 11304 |
| 5 | 257400 |
| 6 | 6881160 |
| 7 | 211170960 |
| 8 | 7315701120 |
| 9 | 282398538240 |
| 10 | 12019910112000 |
| 11 | 559278036979200 |
| 12 | 28242651241728000 |
| 13 | 1538394175334016000 |
| 14 | 89912239244860032000 |
| 15 | 5612575361948755200000 |
| 16 | 372687441873534627840000 |
| 17 | 26231028469670851706880000 |
[1,4,41,602,11304,257400,6881160,211170960, 7315701120,282398538240,12019910112000, 559278036979200,28242651241728000, 1538394175334016000,89912239244860032000, 5612575361948755200000,372687441873534627840000, 26231028469670851706880000] |