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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 18 |
| 4 | 53 |
| 5 | 154 |
| 6 | 443 |
| 7 | 1264 |
| 8 | 3582 |
| 9 | 10092 |
| 10 | 28291 |
| 11 | 78962 |
| 12 | 219541 |
| 13 | 608318 |
| 14 | 1680438 |
| 15 | 4629414 |
| 16 | 12722033 |
| 17 | 34882954 |
| 18 | 95451407 |
| 19 | 260698732 |
| 20 | 710802606 |
| 21 | 1934955072 |
| 22 | 5259642751 |
| 23 | 14277467618 |
| 24 | 38707663273 |
| 25 | 104816737274 |
| 26 | 283521290598 |
| 27 | 766112145594 |
| 28 | 2068131437357 |
[1,2,6,18,53,154,443,1264,3582,10092,28291,78962, 219541,608318,1680438,4629414,12722033,34882954, 95451407,260698732,710802606,1934955072, 5259642751,14277467618,38707663273,104816737274, 283521290598,766112145594,2068131437357] |