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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 2 |
| 3 | 6 |
| 4 | 18 |
| 5 | 78 |
| 6 | 378 |
| 7 | 2214 |
| 8 | 14562 |
| 9 | 108702 |
| 10 | 897642 |
| 11 | 8171766 |
| 12 | 81066258 |
| 13 | 871695918 |
| 14 | 10091490138 |
| 15 | 125189658054 |
| 16 | 1656458307522 |
| 17 | 23288226400062 |
| 18 | 346663764078282 |
| 19 | 5447099463010326 |
| 20 | 90094171024954098 |
| 21 | 1564653992673809358 |
| 22 | 28467075416816935098 |
| 23 | 541467979789775621094 |
[1,2,2,6,18,78,378,2214,14562,108702,897642, 8171766,81066258,871695918,10091490138, 125189658054,1656458307522,23288226400062, 346663764078282,5447099463010326, 90094171024954098,1564653992673809358, 28467075416816935098,541467979789775621094] |