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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 20 |
| 5 | 71 |
| 6 | 259 |
| 7 | 960 |
| 8 | 3597 |
| 9 | 13586 |
| 10 | 51635 |
| 11 | 197223 |
| 12 | 756380 |
| 13 | 2910707 |
| 14 | 11233311 |
| 15 | 43460144 |
| 16 | 168502849 |
| 17 | 654547456 |
| 18 | 2546819347 |
| 19 | 9924285801 |
| 20 | 38723794820 |
| 21 | 151278566731 |
| 22 | 591628491483 |
| 23 | 2316065644414 |
| 24 | 9074988880769 |
| 25 | 35587925333525 |
| 26 | 139666503235814 |
| 27 | 548516611541343 |
[0,1,2,6,20,71,259,960,3597,13586,51635,197223, 756380,2910707,11233311,43460144,168502849, 654547456,2546819347,9924285801,38723794820, 151278566731,591628491483,2316065644414, 9074988880769,35587925333525,139666503235814, 548516611541343] |