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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 721 |
| 7 | 5054 |
| 8 | 40488 |
| 9 | 364896 |
| 10 | 3654000 |
| 11 | 40249441 |
| 12 | 483659508 |
| 13 | 6296246424 |
| 14 | 88269037584 |
| 15 | 1325861901000 |
| 16 | 21243052172161 |
| 17 | 361630022931666 |
| 18 | 6518319228715302 |
| 19 | 124018898163736536 |
| 20 | 2483799332459535000 |
| 21 | 52231733840672804881 |
| 22 | 1150683180739820615582 |
| 23 | 26502219276887376327696 |
[1,1,2,6,24,120,721,5054,40488,364896,3654000, 40249441,483659508,6296246424,88269037584, 1325861901000,21243052172161,361630022931666, 6518319228715302,124018898163736536, 2483799332459535000,52231733840672804881, 1150683180739820615582,26502219276887376327696] |