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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 6 |
| 5 | 33 |
| 6 | 168 |
| 7 | 810 |
| 8 | 3780 |
| 9 | 17226 |
| 10 | 77112 |
| 11 | 340443 |
| 12 | 1486458 |
| 13 | 6431643 |
| 14 | 27619056 |
| 15 | 117846900 |
| 16 | 500088168 |
| 17 | 2112085044 |
| 18 | 8883220752 |
| 19 | 37225117269 |
| 20 | 155483824590 |
| 21 | 647540441397 |
| 22 | 2689724482776 |
| 23 | 11145934772190 |
| 24 | 46087885526508 |
[0,0,1,6,33,168,810,3780,17226,77112,340443, 1486458,6431643,27619056,117846900,500088168, 2112085044,8883220752,37225117269,155483824590, 647540441397,2689724482776,11145934772190, 46087885526508] |