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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 1 |
| 3 | 4 |
| 4 | 10 |
| 5 | 36 |
| 6 | 108 |
| 7 | 392 |
| 8 | 1363 |
| 9 | 5000 |
| 10 | 18223 |
| 11 | 67792 |
| 12 | 252938 |
| 13 | 952540 |
| 14 | 3602478 |
| 15 | 13699554 |
| 16 | 52296713 |
| 17 | 200406388 |
| 18 | 770411478 |
| 19 | 2970401696 |
| 20 | 11482395526 |
| 21 | 44491881090 |
| 22 | 172766311857 |
| 23 | 672186650116 |
[2,1,4,10,36,108,392,1363,5000,18223,67792,252938, 952540,3602478,13699554,52296713,200406388, 770411478,2970401696,11482395526,44491881090, 172766311857,672186650116] |