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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 7 |
| 3 | 56 |
| 4 | 538 |
| 5 | 6124 |
| 6 | 81048 |
| 7 | 1226112 |
| 8 | 20902992 |
| 9 | 396857376 |
| 10 | 8308373760 |
| 11 | 190212376320 |
| 12 | 4728556327680 |
| 13 | 126865966625280 |
| 14 | 3654264347274240 |
| 15 | 112484501485977600 |
| 16 | 3685202487258163200 |
| 17 | 128039255560187596800 |
[0,1,7,56,538,6124,81048,1226112,20902992, 396857376,8308373760,190212376320,4728556327680, 126865966625280,3654264347274240, 112484501485977600,3685202487258163200, 128039255560187596800] |