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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 20 |
| 5 | 66 |
| 6 | 216 |
| 7 | 706 |
| 8 | 2308 |
| 9 | 7546 |
| 10 | 24672 |
| 11 | 80666 |
| 12 | 263740 |
| 13 | 862306 |
| 14 | 2819336 |
| 15 | 9217906 |
| 16 | 30138228 |
| 17 | 98537866 |
| 18 | 322172592 |
| 19 | 1053353226 |
| 20 | 3443970860 |
| 21 | 11260168946 |
| 22 | 36815469656 |
| 23 | 120369313506 |
| 24 | 393551182948 |
| 25 | 1286727730586 |
| 26 | 4206996000512 |
[1,1,2,6,20,66,216,706,2308,7546,24672,80666, 263740,862306,2819336,9217906,30138228,98537866, 322172592,1053353226,3443970860,11260168946, 36815469656,120369313506,393551182948, 1286727730586,4206996000512] |