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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 8 |
| 5 | 18 |
| 6 | 54 |
| 7 | 155 |
| 8 | 500 |
| 9 | 1614 |
| 10 | 5456 |
| 11 | 18630 |
| 12 | 64960 |
| 13 | 228740 |
| 14 | 814914 |
| 15 | 2926323 |
| 16 | 10589916 |
| 17 | 38561814 |
| 18 | 141219432 |
| 19 | 519711666 |
| 20 | 1921142832 |
| 21 | 7129756188 |
| 22 | 26555149404 |
| 23 | 99228108222 |
| 24 | 371886574632 |
| 25 | 1397548389644 |
| 26 | 5265131346368 |
[1,1,2,3,8,18,54,155,500,1614,5456,18630,64960, 228740,814914,2926323,10589916,38561814,141219432, 519711666,1921142832,7129756188,26555149404, 99228108222,371886574632,1397548389644, 5265131346368] |