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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 68 |
| 4 | 286 |
| 5 | 6760 |
| 6 | 28122 |
| 7 | 662508 |
| 8 | 2755766 |
| 9 | 64919120 |
| 10 | 270037042 |
| 11 | 6361411348 |
| 12 | 26460874446 |
| 13 | 623353393080 |
| 14 | 2592895658762 |
| 15 | 61082271110588 |
| 16 | 254077313684326 |
| 17 | 5985439215444640 |
| 18 | 24896983845405282 |
| 19 | 586511960842464228 |
| 20 | 2439650339536033406 |
[0,2,68,286,6760,28122,662508,2755766,64919120, 270037042,6361411348,26460874446,623353393080, 2592895658762,61082271110588,254077313684326, 5985439215444640,24896983845405282, 586511960842464228,2439650339536033406] |