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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 73 |
| 5 | 276 |
| 6 | 1090 |
| 7 | 4416 |
| 8 | 18242 |
| 9 | 76675 |
| 10 | 326150 |
| 11 | 1403464 |
| 12 | 6091537 |
| 13 | 26654395 |
| 14 | 117412325 |
| 15 | 520268068 |
| 16 | 2317636972 |
| 17 | 10371361869 |
| 18 | 46608781873 |
| 19 | 210226515573 |
| 20 | 951461046417 |
| 21 | 4319309714478 |
| 22 | 19663072521834 |
| 23 | 89743573185081 |
| 24 | 410552491858376 |
| 25 | 1882274544712750 |
| 26 | 8646913270639666 |
| 27 | 39797115879839132 |
[1,2,6,20,73,276,1090,4416,18242,76675,326150, 1403464,6091537,26654395,117412325,520268068, 2317636972,10371361869,46608781873,210226515573, 951461046417,4319309714478,19663072521834, 89743573185081,410552491858376,1882274544712750, 8646913270639666,39797115879839132] |