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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 56 |
| 3 | 396 |
| 4 | 2040 |
| 5 | 9130 |
| 6 | 37944 |
| 7 | 151172 |
| 8 | 586608 |
| 9 | 2235618 |
| 10 | 8407640 |
| 11 | 31292844 |
| 12 | 115494312 |
| 13 | 423283562 |
| 14 | 1542120664 |
| 15 | 5589611460 |
| 16 | 20170172896 |
| 17 | 72499928322 |
| 18 | 259692909048 |
| 19 | 927342338956 |
| 20 | 3302291258200 |
| 21 | 11730149911914 |
| 22 | 41572470711288 |
| 23 | 147031327493572 |
| 24 | 519029653663056 |
[2,56,396,2040,9130,37944,151172,586608,2235618, 8407640,31292844,115494312,423283562,1542120664, 5589611460,20170172896,72499928322,259692909048, 927342338956,3302291258200,11730149911914, 41572470711288,147031327493572,519029653663056] |