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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 8 |
| 5 | 41 |
| 6 | 120 |
| 7 | 826 |
| 8 | 4602 |
| 9 | 47570 |
| 10 | 473649 |
| 11 | 10093040 |
| 12 | 203861263 |
| 13 | 8821354950 |
| 14 | 467680021214 |
| 15 | 51343335981422 |
| 16 | 7427745026671872 |
| 17 | 2637938775610253117 |
| 18 | 1315874983271581469522 |
| 19 | 1773440184382265096424766 |
| 20 | 4023316751814245493054773044 |
| 21 | 26037772294065481552999203782248 |
[0,1,1,4,8,41,120,826,4602,47570,473649,10093040, 203861263,8821354950,467680021214,51343335981422, 7427745026671872,2637938775610253117, 1315874983271581469522,1773440184382265096424766, 4023316751814245493054773044, 26037772294065481552999203782248] |