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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 3 |
| 3 | 3 |
| 4 | 15 |
| 5 | 45 |
| 6 | 198 |
| 7 | 972 |
| 8 | 5652 |
| 9 | 37881 |
| 10 | 289548 |
| 11 | 2492640 |
| 12 | 23906475 |
| 13 | 253012653 |
| 14 | 2930556024 |
| 15 | 36883817127 |
| 16 | 501315357690 |
| 17 | 7318715960511 |
| 18 | 114224260779891 |
| 19 | 1897913866979529 |
| 20 | 33449523840512127 |
| 21 | 623265596538965334 |
| 22 | 12241892922194658510 |
| 23 | 252793167644378784006 |
[1,0,3,3,15,45,198,972,5652,37881,289548,2492640, 23906475,253012653,2930556024,36883817127, 501315357690,7318715960511,114224260779891, 1897913866979529,33449523840512127, 623265596538965334,12241892922194658510, 252793167644378784006] |