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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 20 |
| 5 | 55 |
| 6 | 126 |
| 7 | 301 |
| 8 | 680 |
| 9 | 1539 |
| 10 | 3410 |
| 11 | 7513 |
| 12 | 16380 |
| 13 | 35503 |
| 14 | 76454 |
| 15 | 163845 |
| 16 | 349520 |
| 17 | 742747 |
| 18 | 1572858 |
| 19 | 3320497 |
| 20 | 6990500 |
| 21 | 14680071 |
| 22 | 30758222 |
| 23 | 64312669 |
| 24 | 134217720 |
| 25 | 279620275 |
| 26 | 581610146 |
| 27 | 1207959561 |
| 28 | 2505397580 |
| 29 | 5189752159 |
[0,1,2,9,20,55,126,301,680,1539,3410,7513,16380, 35503,76454,163845,349520,742747,1572858,3320497, 6990500,14680071,30758222,64312669,134217720, 279620275,581610146,1207959561,2505397580, 5189752159] |