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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 20 |
| 3 | 140 |
| 4 | 863 |
| 5 | 4962 |
| 6 | 27313 |
| 7 | 145932 |
| 8 | 763031 |
| 9 | 3924694 |
| 10 | 19928429 |
| 11 | 100145056 |
| 12 | 498967875 |
| 13 | 2468341930 |
| 14 | 12136538329 |
| 15 | 59362244596 |
| 16 | 289033801519 |
| 17 | 1401690320766 |
| 18 | 6773621702213 |
| 19 | 32630424771912 |
| 20 | 156746889564187 |
| 21 | 751052250017618 |
[2,20,140,863,4962,27313,145932,763031,3924694, 19928429,100145056,498967875,2468341930, 12136538329,59362244596,289033801519, 1401690320766,6773621702213,32630424771912, 156746889564187,751052250017618] |