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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 13 |
| 4 | 55 |
| 5 | 219 |
| 6 | 947 |
| 7 | 4124 |
| 8 | 18509 |
| 9 | 83805 |
| 10 | 385192 |
| 11 | 1784012 |
| 12 | 8336935 |
| 13 | 39189722 |
| 14 | 185289101 |
| 15 | 880043266 |
| 16 | 4197296943 |
| 17 | 20088159938 |
| 18 | 96442832029 |
| 19 | 464273089991 |
| 20 | 2240451018858 |
| 21 | 10835127441925 |
| 22 | 52501963913485 |
| 23 | 254843969483289 |
| 24 | 1238967647764672 |
| 25 | 6032102693466452 |
| 26 | 29406664336282397 |
| 27 | 143529821637417576 |
[1,1,4,13,55,219,947,4124,18509,83805,385192, 1784012,8336935,39189722,185289101,880043266, 4197296943,20088159938,96442832029,464273089991, 2240451018858,10835127441925,52501963913485, 254843969483289,1238967647764672,6032102693466452, 29406664336282397,143529821637417576] |