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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 18 |
| 4 | 146 |
| 5 | 1530 |
| 6 | 19620 |
| 7 | 297360 |
| 8 | 5201784 |
| 9 | 103146120 |
| 10 | 2286181800 |
| 11 | 56011087440 |
| 12 | 1503057473280 |
| 13 | 43844234353920 |
| 14 | 1381310964633600 |
| 15 | 46743301840435200 |
| 16 | 1690919874777893760 |
| 17 | 65116170597269151360 |
| 18 | 2659604669692822051200 |
| 19 | 114838104572526535200000 |
| 20 | 5226654647185285702752000 |
[1,1,3,18,146,1530,19620,297360,5201784,103146120, 2286181800,56011087440,1503057473280, 43844234353920,1381310964633600,46743301840435200, 1690919874777893760,65116170597269151360, 2659604669692822051200,114838104572526535200000, 5226654647185285702752000] |