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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 5 |
| 3 | 38 |
| 4 | 222 |
| 5 | 1974 |
| 6 | 14640 |
| 7 | 154580 |
| 8 | 1476720 |
| 9 | 17753400 |
| 10 | 205430400 |
| 11 | 2924030592 |
| 12 | 38559628800 |
| 13 | 623916216000 |
| 14 | 9701871379200 |
| 15 | 172359487872000 |
| 16 | 3007238402488320 |
| 17 | 60362232844193280 |
| 18 | 1161408374590464000 |
| 19 | 25603215951785472000 |
| 20 | 547592177551491072000 |
| 21 | 12990145748633044992000 |
[1,5,38,222,1974,14640,154580,1476720,17753400, 205430400,2924030592,38559628800,623916216000, 9701871379200,172359487872000,3007238402488320, 60362232844193280,1161408374590464000, 25603215951785472000,547592177551491072000, 12990145748633044992000] |