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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 3 |
| 3 | 1 |
| 4 | 21 |
| 5 | 26 |
| 6 | 215 |
| 7 | 498 |
| 8 | 2821 |
| 9 | 9040 |
| 10 | 43695 |
| 11 | 165375 |
| 12 | 752785 |
| 13 | 3101970 |
| 14 | 13881803 |
| 15 | 59837183 |
| 16 | 267860685 |
| 17 | 1184749704 |
| 18 | 5337504263 |
| 19 | 23996776941 |
| 20 | 108964583121 |
| 21 | 495544446410 |
| 22 | 2267450194443 |
| 23 | 10402298479276 |
| 24 | 47926692348121 |
[1,0,3,1,21,26,215,498,2821,9040,43695,165375, 752785,3101970,13881803,59837183,267860685, 1184749704,5337504263,23996776941,108964583121, 495544446410,2267450194443,10402298479276, 47926692348121] |