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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 20 |
| 2 | 380 |
| 3 | 7220 |
| 4 | 136820 |
| 5 | 2593100 |
| 6 | 49121660 |
| 7 | 930556460 |
| 8 | 17625825740 |
| 9 | 333857601020 |
| 10 | 6323384122580 |
| 11 | 119767717450100 |
| 12 | 2268399952520660 |
| 13 | 42963566150826380 |
| 14 | 813721674662589980 |
| 15 | 15411746407417290020 |
| 16 | 291893918240586194660 |
| 17 | 5528387235193561980740 |
[1,20,380,7220,136820,2593100,49121660,930556460, 17625825740,333857601020,6323384122580, 119767717450100,2268399952520660, 42963566150826380,813721674662589980, 15411746407417290020,291893918240586194660, 5528387235193561980740] |