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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 480 |
| 7 | 1632 |
| 8 | 5124 |
| 9 | 15860 |
| 10 | 50186 |
| 11 | 158808 |
| 12 | 496472 |
| 13 | 1526736 |
| 14 | 4627392 |
| 15 | 13908192 |
| 16 | 41570256 |
| 17 | 123658616 |
| 18 | 366072856 |
| 19 | 1078360714 |
| 20 | 3162222448 |
| 21 | 9236396440 |
| 22 | 26885780412 |
| 23 | 78022705424 |
| 24 | 225793573676 |
| 25 | 651761629560 |
| 26 | 1876905701372 |
[1,2,6,24,120,480,1632,5124,15860,50186,158808, 496472,1526736,4627392,13908192,41570256, 123658616,366072856,1078360714,3162222448, 9236396440,26885780412,78022705424,225793573676, 651761629560,1876905701372] |