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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 43 |
| 5 | 142 |
| 6 | 508 |
| 7 | 1781 |
| 8 | 6414 |
| 9 | 23124 |
| 10 | 84296 |
| 11 | 308613 |
| 12 | 1137129 |
| 13 | 4207456 |
| 14 | 15636927 |
| 15 | 58322808 |
| 16 | 218272766 |
| 17 | 819319778 |
| 18 | 3083913810 |
| 19 | 11636761924 |
| 20 | 44010780075 |
| 21 | 166802192488 |
| 22 | 633420816341 |
| 23 | 2409731688860 |
| 24 | 9182826866499 |
| 25 | 35048239457878 |
| 26 | 133965833871427 |
[1,1,4,12,43,142,508,1781,6414,23124,84296,308613, 1137129,4207456,15636927,58322808,218272766, 819319778,3083913810,11636761924,44010780075, 166802192488,633420816341,2409731688860, 9182826866499,35048239457878,133965833871427] |