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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 20 |
| 6 | 72 |
| 7 | 270 |
| 8 | 1049 |
| 9 | 4176 |
| 10 | 16962 |
| 11 | 69990 |
| 12 | 292608 |
| 13 | 1236718 |
| 14 | 5275724 |
| 15 | 22685636 |
| 16 | 98225447 |
| 17 | 427888458 |
| 18 | 1873979814 |
| 19 | 8246535936 |
| 20 | 36444747110 |
| 21 | 161685649174 |
| 22 | 719819353928 |
| 23 | 3214805630688 |
| 24 | 14399464322254 |
| 25 | 64668729869542 |
[1,1,2,6,20,72,270,1049,4176,16962,69990,292608, 1236718,5275724,22685636,98225447,427888458, 1873979814,8246535936,36444747110,161685649174, 719819353928,3214805630688,14399464322254, 64668729869542] |