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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 24 |
| 4 | 115 |
| 5 | 618 |
| 6 | 3591 |
| 7 | 22088 |
| 8 | 141903 |
| 9 | 943590 |
| 10 | 6452490 |
| 11 | 45159480 |
| 12 | 322305165 |
| 13 | 2339100078 |
| 14 | 17223121350 |
| 15 | 128428689888 |
| 16 | 968383277791 |
| 17 | 7374380672718 |
| 18 | 56655414930642 |
| 19 | 438741242896680 |
| 20 | 3422125459579869 |
| 21 | 26866961380274598 |
| 22 | 212191772351034249 |
| 23 | 1685036376746788392 |
[1,2,6,24,115,618,3591,22088,141903,943590, 6452490,45159480,322305165,2339100078,17223121350, 128428689888,968383277791,7374380672718, 56655414930642,438741242896680,3422125459579869, 26866961380274598,212191772351034249, 1685036376746788392] |