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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 72 |
| 5 | 264 |
| 6 | 984 |
| 7 | 3714 |
| 8 | 14148 |
| 9 | 54284 |
| 10 | 209482 |
| 11 | 812196 |
| 12 | 3161340 |
| 13 | 12345658 |
| 14 | 48348522 |
| 15 | 189807336 |
| 16 | 746740510 |
| 17 | 2943359208 |
| 18 | 11620961412 |
| 19 | 45950375602 |
| 20 | 181936110006 |
| 21 | 721233025332 |
| 22 | 2862271873966 |
| 23 | 11370584735100 |
| 24 | 45212101270728 |
| 25 | 179926167512914 |
[1,2,6,20,72,264,984,3714,14148,54284,209482, 812196,3161340,12345658,48348522,189807336, 746740510,2943359208,11620961412,45950375602, 181936110006,721233025332,2862271873966, 11370584735100,45212101270728,179926167512914] |