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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 4 |
| 6 | 18 |
| 7 | 54 |
| 8 | 384 |
| 9 | 1920 |
| 10 | 15000 |
| 11 | 108000 |
| 12 | 1270080 |
| 13 | 8890560 |
| 14 | 126443520 |
| 15 | 1440270720 |
| 16 | 18811699200 |
| 17 | 232243200000 |
| 18 | 4303470124800 |
| 19 | 56336336179200 |
| 20 | 1165698293760000 |
| 21 | 17784994106880000 |
| 22 | 349410939842764800 |
| 23 | 6977881195084800000 |
| 24 | 173541988447027200000 |
[1,1,1,1,2,4,18,54,384,1920,15000,108000,1270080, 8890560,126443520,1440270720,18811699200, 232243200000,4303470124800,56336336179200, 1165698293760000,17784994106880000, 349410939842764800,6977881195084800000, 173541988447027200000] |