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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 30 |
| 5 | 150 |
| 6 | 900 |
| 7 | 7020 |
| 8 | 62460 |
| 9 | 562140 |
| 10 | 5984280 |
| 11 | 67252680 |
| 12 | 863165160 |
| 13 | 11700148680 |
| 14 | 173098134000 |
| 15 | 2625661170000 |
| 16 | 45310413258000 |
| 17 | 782198417206800 |
| 18 | 14310269286746400 |
| 19 | 280333959468789600 |
| 20 | 6002139207488767200 |
| 21 | 129820528515538159200 |
| 22 | 2934651197018947982400 |
[1,1,2,6,30,150,900,7020,62460,562140,5984280, 67252680,863165160,11700148680,173098134000, 2625661170000,45310413258000,782198417206800, 14310269286746400,280333959468789600, 6002139207488767200,129820528515538159200, 2934651197018947982400] |