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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 9 |
| 5 | 45 |
| 6 | 237 |
| 7 | 1335 |
| 8 | 7767 |
| 9 | 45867 |
| 10 | 275865 |
| 11 | 1681776 |
| 12 | 10373614 |
| 13 | 64620952 |
| 14 | 405996375 |
| 15 | 2569673028 |
| 16 | 16369919346 |
| 17 | 104880810464 |
| 18 | 675383823982 |
| 19 | 4368948815362 |
| 20 | 28377658731830 |
| 21 | 185003199176340 |
| 22 | 1210146671320603 |
| 23 | 7940083938945628 |
| 24 | 52243075940256372 |
[0,1,1,1,9,45,237,1335,7767,45867,275865,1681776, 10373614,64620952,405996375,2569673028, 16369919346,104880810464,675383823982, 4368948815362,28377658731830,185003199176340, 1210146671320603,7940083938945628, 52243075940256372] |