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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 18 |
| 4 | 56 |
| 5 | 180 |
| 6 | 594 |
| 7 | 2002 |
| 8 | 6864 |
| 9 | 23868 |
| 10 | 83980 |
| 11 | 298452 |
| 12 | 1069776 |
| 13 | 3863080 |
| 14 | 14040810 |
| 15 | 51325650 |
| 16 | 188574240 |
| 17 | 695987820 |
| 18 | 2579248980 |
| 19 | 9593714460 |
| 20 | 35804293200 |
| 21 | 134032593240 |
| 22 | 503154100020 |
| 23 | 1893689067348 |
| 24 | 7144084508256 |
[1,2,6,18,56,180,594,2002,6864,23868,83980,298452, 1069776,3863080,14040810,51325650,188574240, 695987820,2579248980,9593714460,35804293200, 134032593240,503154100020,1893689067348, 7144084508256] |