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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 28 |
| 4 | 271 |
| 5 | 1567 |
| 6 | 6616 |
| 7 | 21925 |
| 8 | 60481 |
| 9 | 164836 |
| 10 | 627751 |
| 11 | 3355183 |
| 12 | 18052336 |
| 13 | 84393037 |
| 14 | 338279761 |
| 15 | 1198269100 |
| 16 | 4009627711 |
| 17 | 14134316671 |
| 18 | 57201128776 |
| 19 | 256878349813 |
| 20 | 1159252365601 |
| 21 | 4930744442932 |
| 22 | 19479046111831 |
[1,1,1,28,271,1567,6616,21925,60481,164836,627751, 3355183,18052336,84393037,338279761,1198269100, 4009627711,14134316671,57201128776,256878349813, 1159252365601,4930744442932,19479046111831] |