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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 17 |
| 6 | 53 |
| 7 | 205 |
| 8 | 871 |
| 9 | 3876 |
| 10 | 18820 |
| 11 | 99585 |
| 12 | 558847 |
| 13 | 3313117 |
| 14 | 20825145 |
| 15 | 138046940 |
| 16 | 959298572 |
| 17 | 6974868139 |
| 18 | 52972352923 |
| 19 | 419104459913 |
| 20 | 3446343893607 |
| 21 | 29405917751526 |
| 22 | 259930518212766 |
| 23 | 2376498296500063 |
| 24 | 22441988298860757 |
| 25 | 218615700758838253 |
[1,1,1,2,6,17,53,205,871,3876,18820,99585,558847, 3313117,20825145,138046940,959298572,6974868139, 52972352923,419104459913,3446343893607, 29405917751526,259930518212766,2376498296500063, 22441988298860757,218615700758838253] |