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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 4 |
| 6 | 10 |
| 7 | 28 |
| 8 | 77 |
| 9 | 221 |
| 10 | 650 |
| 11 | 1951 |
| 12 | 5920 |
| 13 | 18211 |
| 14 | 56509 |
| 15 | 176919 |
| 16 | 557786 |
| 17 | 1769966 |
| 18 | 5647568 |
| 19 | 18110734 |
| 20 | 58335561 |
| 21 | 188658338 |
| 22 | 612337013 |
| 23 | 1994058293 |
| 24 | 6513153445 |
| 25 | 21332562178 |
| 26 | 70048092196 |
| 27 | 230550762108 |
| 28 | 760462920317 |
[1,1,1,2,4,10,28,77,221,650,1951,5920,18211,56509, 176919,557786,1769966,5647568,18110734,58335561, 188658338,612337013,1994058293,6513153445, 21332562178,70048092196,230550762108,760462920317] |