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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 108 |
| 6 | 504 |
| 7 | 2376 |
| 8 | 11232 |
| 9 | 53136 |
| 10 | 251424 |
| 11 | 1189728 |
| 12 | 5629824 |
| 13 | 26640576 |
| 14 | 126064512 |
| 15 | 596543616 |
| 16 | 2822874624 |
| 17 | 13357986048 |
| 18 | 63210668544 |
| 19 | 299116094976 |
| 20 | 1415432558592 |
| 21 | 6697898781696 |
| 22 | 31694797338624 |
| 23 | 149981391341568 |
| 24 | 709719564017664 |
| 25 | 3358429036056576 |
[1,1,2,6,24,108,504,2376,11232,53136,251424, 1189728,5629824,26640576,126064512,596543616, 2822874624,13357986048,63210668544,299116094976, 1415432558592,6697898781696,31694797338624, 149981391341568,709719564017664,3358429036056576] |