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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 4 |
| 4 | 13 |
| 5 | 63 |
| 6 | 264 |
| 7 | 1005 |
| 8 | 4113 |
| 9 | 16720 |
| 10 | 67541 |
| 11 | 273173 |
| 12 | 1105028 |
| 13 | 4470455 |
| 14 | 18086203 |
| 15 | 73164414 |
| 16 | 295979201 |
| 17 | 1197372779 |
| 18 | 4843899390 |
| 19 | 19595676337 |
| 20 | 79273069299 |
| 21 | 320694228442 |
| 22 | 1297348415225 |
| 23 | 5248341466951 |
| 24 | 21231835277428 |
| 25 | 85892055453779 |
[0,2,4,13,63,264,1005,4113,16720,67541,273173, 1105028,4470455,18086203,73164414,295979201, 1197372779,4843899390,19595676337,79273069299, 320694228442,1297348415225,5248341466951, 21231835277428,85892055453779] |