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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 7 |
| 5 | 27 |
| 6 | 142 |
| 7 | 834 |
| 8 | 5962 |
| 9 | 46788 |
| 10 | 426708 |
| 11 | 4198632 |
| 12 | 46516800 |
| 13 | 551415936 |
| 14 | 7197404976 |
| 15 | 99712618560 |
| 16 | 1500173940960 |
| 17 | 23786129681280 |
| 18 | 405087689727360 |
| 19 | 7237524061198080 |
| 20 | 137652562628778240 |
| 21 | 2735042530132523520 |
| 22 | 57482464477451489280 |
| 23 | 1257272784581092070400 |
[1,1,1,2,7,27,142,834,5962,46788,426708,4198632, 46516800,551415936,7197404976,99712618560, 1500173940960,23786129681280,405087689727360, 7237524061198080,137652562628778240, 2735042530132523520,57482464477451489280, 1257272784581092070400] |