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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 8 |
| 6 | 20 |
| 7 | 44 |
| 8 | 124 |
| 9 | 300 |
| 10 | 920 |
| 11 | 2420 |
| 12 | 7940 |
| 13 | 22460 |
| 14 | 78040 |
| 15 | 235260 |
| 16 | 859580 |
| 17 | 2741660 |
| 18 | 10477880 |
| 19 | 35152820 |
| 20 | 139931620 |
| 21 | 491459820 |
| 22 | 2030707640 |
| 23 | 7436765660 |
| 24 | 31805257340 |
| 25 | 121046445260 |
| 26 | 534514790680 |
| 27 | 2108118579060 |
| 28 | 9591325648580 |
[0,1,1,2,4,8,20,44,124,300,920,2420,7940,22460, 78040,235260,859580,2741660,10477880,35152820, 139931620,491459820,2030707640,7436765660, 31805257340,121046445260,534514790680, 2108118579060,9591325648580] |