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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 9 |
| 5 | 46 |
| 6 | 262 |
| 7 | 1588 |
| 8 | 10053 |
| 9 | 65686 |
| 10 | 439658 |
| 11 | 2999116 |
| 12 | 20774154 |
| 13 | 145726348 |
| 14 | 1033125004 |
| 15 | 7390626280 |
| 16 | 53281906861 |
| 17 | 386732675046 |
| 18 | 2823690230850 |
| 19 | 20725376703324 |
| 20 | 152833785130398 |
| 21 | 1131770853856100 |
| 22 | 8412813651862868 |
[0,0,1,2,9,46,262,1588,10053,65686,439658,2999116, 20774154,145726348,1033125004,7390626280, 53281906861,386732675046,2823690230850, 20725376703324,152833785130398,1131770853856100, 8412813651862868] |