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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 13 |
| 5 | 68 |
| 6 | 373 |
| 7 | 2528 |
| 8 | 19097 |
| 9 | 160400 |
| 10 | 1522409 |
| 11 | 15384128 |
| 12 | 174263717 |
| 13 | 2066458176 |
| 14 | 27072485469 |
| 15 | 369136141824 |
| 16 | 5477315064625 |
| 17 | 84457146691840 |
| 18 | 1398343023229393 |
| 19 | 24053254928131072 |
| 20 | 439386703590146365 |
[1,1,1,4,13,68,373,2528,19097,160400,1522409, 15384128,174263717,2066458176,27072485469, 369136141824,5477315064625,84457146691840, 1398343023229393,24053254928131072, 439386703590146365] |