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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 16 |
| 5 | 60 |
| 6 | 144 |
| 7 | 672 |
| 8 | 1536 |
| 9 | 6480 |
| 10 | 19200 |
| 11 | 76032 |
| 12 | 165888 |
| 13 | 1048320 |
| 14 | 2257920 |
| 15 | 8294400 |
| 16 | 28311552 |
| 17 | 126904320 |
| 18 | 268738560 |
| 19 | 1470873600 |
| 20 | 3096576000 |
| 21 | 16094453760 |
| 22 | 51385466880 |
| 23 | 175814737920 |
| 24 | 366917713920 |
| 25 | 2717245440000 |
| 26 | 6782244618240 |
| 27 | 22754631352320 |
| 28 | 69918208819200 |
[1,1,2,6,16,60,144,672,1536,6480,19200,76032, 165888,1048320,2257920,8294400,28311552,126904320, 268738560,1470873600,3096576000,16094453760, 51385466880,175814737920,366917713920, 2717245440000,6782244618240,22754631352320, 69918208819200] |