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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 7 |
| 5 | 18 |
| 6 | 58 |
| 7 | 180 |
| 8 | 613 |
| 9 | 2076 |
| 10 | 7270 |
| 11 | 25752 |
| 12 | 92918 |
| 13 | 338432 |
| 14 | 1246092 |
| 15 | 4624536 |
| 16 | 17290646 |
| 17 | 65047436 |
| 18 | 246079536 |
| 19 | 935484928 |
| 20 | 3571960668 |
| 21 | 13692523960 |
| 22 | 52675401248 |
| 23 | 203299385584 |
| 24 | 786949008100 |
| 25 | 3054440440486 |
| 26 | 11884949139900 |
| 27 | 46351113658232 |
| 28 | 181153317512536 |
[1,1,2,7,18,58,180,613,2076,7270,25752,92918, 338432,1246092,4624536,17290646,65047436, 246079536,935484928,3571960668,13692523960, 52675401248,203299385584,786949008100, 3054440440486,11884949139900,46351113658232, 181153317512536] |