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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 5 |
| 4 | 17 |
| 5 | 75 |
| 6 | 407 |
| 7 | 2621 |
| 8 | 19524 |
| 9 | 165090 |
| 10 | 1561900 |
| 11 | 16345264 |
| 12 | 187452475 |
| 13 | 2337729329 |
| 14 | 31497068553 |
| 15 | 455930417721 |
| 16 | 7056447326642 |
| 17 | 116279714536838 |
| 18 | 2032547040624336 |
| 19 | 37563420959431569 |
| 20 | 731810131489893185 |
| 21 | 14989602024463575408 |
| 22 | 322032777284323744894 |
| 23 | 7240745954488939549295 |
[1,1,2,5,17,75,407,2621,19524,165090,1561900, 16345264,187452475,2337729329,31497068553, 455930417721,7056447326642,116279714536838, 2032547040624336,37563420959431569, 731810131489893185,14989602024463575408, 322032777284323744894,7240745954488939549295] |