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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 54 |
| 5 | 156 |
| 6 | 444 |
| 7 | 1192 |
| 8 | 3174 |
| 9 | 8620 |
| 10 | 22516 |
| 11 | 58392 |
| 12 | 151996 |
| 13 | 387352 |
| 14 | 984888 |
| 15 | 2507088 |
| 16 | 6270854 |
| 17 | 15659724 |
| 18 | 39067588 |
| 19 | 96454072 |
| 20 | 237663444 |
| 21 | 584266696 |
| 22 | 1425921992 |
| 23 | 3470869296 |
| 24 | 8431325916 |
| 25 | 20380759544 |
| 26 | 49122457608 |
| 27 | 118178637040 |
| 28 | 283150466232 |
| 29 | 676768288176 |
[1,2,6,20,54,156,444,1192,3174,8620,22516,58392, 151996,387352,984888,2507088,6270854,15659724, 39067588,96454072,237663444,584266696,1425921992, 3470869296,8431325916,20380759544,49122457608, 118178637040,283150466232,676768288176] |