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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 5 |
| 5 | 22 |
| 6 | 117 |
| 7 | 749 |
| 8 | 5550 |
| 9 | 46705 |
| 10 | 439803 |
| 11 | 4581281 |
| 12 | 52302950 |
| 13 | 649428294 |
| 14 | 8713162940 |
| 15 | 125614765717 |
| 16 | 1936560971460 |
| 17 | 31791875948135 |
| 18 | 553708506096682 |
| 19 | 10197464987280555 |
| 20 | 198000778503030765 |
| 21 | 4042515894436878102 |
[1,1,1,2,5,22,117,749,5550,46705,439803,4581281, 52302950,649428294,8713162940,125614765717, 1936560971460,31791875948135,553708506096682, 10197464987280555,198000778503030765, 4042515894436878102] |