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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 718 |
| 7 | 4914 |
| 8 | 37300 |
| 9 | 308460 |
| 10 | 2748354 |
| 11 | 26194542 |
| 12 | 265691456 |
| 13 | 2856606480 |
| 14 | 32449828310 |
| 15 | 388371994890 |
| 16 | 4885210675692 |
| 17 | 64439603536980 |
| 18 | 889564376280586 |
| 19 | 12827733624005958 |
| 20 | 192897097090449208 |
| 21 | 3020051018689640760 |
| 22 | 49155675298520617182 |
| 23 | 830625328754347651746 |
[1,1,2,6,24,120,718,4914,37300,308460,2748354, 26194542,265691456,2856606480,32449828310, 388371994890,4885210675692,64439603536980, 889564376280586,12827733624005958, 192897097090449208,3020051018689640760, 49155675298520617182,830625328754347651746] |