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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 5 |
| 5 | 11 |
| 6 | 30 |
| 7 | 78 |
| 8 | 223 |
| 9 | 658 |
| 10 | 2026 |
| 11 | 6429 |
| 12 | 21015 |
| 13 | 70233 |
| 14 | 239360 |
| 15 | 829224 |
| 16 | 2912947 |
| 17 | 10356334 |
| 18 | 37205121 |
| 19 | 134887153 |
| 20 | 493000086 |
| 21 | 1814902409 |
| 22 | 6724595543 |
| 23 | 25061885217 |
| 24 | 93899071368 |
| 25 | 353514105817 |
| 26 | 1336822098961 |
| 27 | 5075833932200 |
[1,0,1,2,5,11,30,78,223,658,2026,6429,21015,70233, 239360,829224,2912947,10356334,37205121,134887153, 493000086,1814902409,6724595543,25061885217, 93899071368,353514105817,1336822098961, 5075833932200] |