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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 15 |
| 4 | 55 |
| 5 | 200 |
| 6 | 728 |
| 7 | 2652 |
| 8 | 9690 |
| 9 | 35530 |
| 10 | 130750 |
| 11 | 482885 |
| 12 | 1789515 |
| 13 | 6653325 |
| 14 | 24812400 |
| 15 | 92798375 |
| 16 | 347993910 |
| 17 | 1308233790 |
| 18 | 4929576600 |
| 19 | 18615637950 |
| 20 | 70441574000 |
| 21 | 267058714626 |
| 22 | 1014283603024 |
| 23 | 3858687620200 |
| 24 | 14702930414900 |
[0,1,4,15,55,200,728,2652,9690,35530,130750, 482885,1789515,6653325,24812400,92798375, 347993910,1308233790,4929576600,18615637950, 70441574000,267058714626,1014283603024, 3858687620200,14702930414900] |