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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 14 |
| 6 | 45 |
| 7 | 120 |
| 8 | 468 |
| 9 | 1478 |
| 10 | 5208 |
| 11 | 18714 |
| 12 | 67200 |
| 13 | 244208 |
| 14 | 914953 |
| 15 | 3393606 |
| 16 | 12865732 |
| 17 | 48963934 |
| 18 | 187738332 |
| 19 | 724740954 |
| 20 | 2816697570 |
| 21 | 10990919138 |
| 22 | 43152034764 |
| 23 | 170075450764 |
| 24 | 673260699676 |
| 25 | 2675316693314 |
| 26 | 10669114073080 |
| 27 | 42685090123056 |
| 28 | 171316969097872 |
| 29 | 689506156453890 |
| 30 | 2782631094476893 |
[1,0,1,2,4,14,45,120,468,1478,5208,18714,67200, 244208,914953,3393606,12865732,48963934,187738332, 724740954,2816697570,10990919138,43152034764, 170075450764,673260699676,2675316693314, 10669114073080,42685090123056,171316969097872, 689506156453890,2782631094476893] |