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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 12 |
| 6 | 30 |
| 7 | 84 |
| 8 | 238 |
| 9 | 680 |
| 10 | 1993 |
| 11 | 5882 |
| 12 | 17575 |
| 13 | 52976 |
| 14 | 160870 |
| 15 | 491924 |
| 16 | 1512940 |
| 17 | 4677672 |
| 18 | 14529744 |
| 19 | 45320640 |
| 20 | 141897039 |
| 21 | 445792908 |
| 22 | 1404899598 |
| 23 | 4440113940 |
| 24 | 14069493813 |
| 25 | 44689897200 |
| 26 | 142268117566 |
| 27 | 453839997836 |
| 28 | 1450547245960 |
| 29 | 4644492976232 |
| 30 | 14896047099592 |
[1,0,1,2,4,12,30,84,238,680,1993,5882,17575,52976, 160870,491924,1512940,4677672,14529744,45320640, 141897039,445792908,1404899598,4440113940, 14069493813,44689897200,142268117566,453839997836, 1450547245960,4644492976232,14896047099592] |