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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 9 |
| 5 | 66 |
| 6 | 646 |
| 7 | 7760 |
| 8 | 109585 |
| 9 | 1771810 |
| 10 | 32211854 |
| 11 | 649833996 |
| 12 | 14399543754 |
| 13 | 347618918364 |
| 14 | 9080945744920 |
| 15 | 255239884317292 |
| 16 | 7680997048377377 |
| 17 | 246417820289930866 |
| 18 | 8395878803694101510 |
| 19 | 302786064773642534220 |
| 20 | 11523127939987785101646 |
| 21 | 461518291638811484923036 |
[1,1,1,2,9,66,646,7760,109585,1771810,32211854, 649833996,14399543754,347618918364,9080945744920, 255239884317292,7680997048377377, 246417820289930866,8395878803694101510, 302786064773642534220,11523127939987785101646, 461518291638811484923036] |