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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 30 |
| 3 | 138 |
| 4 | 618 |
| 5 | 2730 |
| 6 | 11946 |
| 7 | 51882 |
| 8 | 224130 |
| 9 | 964134 |
| 10 | 4133166 |
| 11 | 17668938 |
| 12 | 75355206 |
| 13 | 320734686 |
| 14 | 1362791250 |
| 15 | 5781765582 |
| 16 | 24497330322 |
| 17 | 103673967882 |
| 18 | 438296739594 |
| 19 | 1851231376374 |
| 20 | 7812439620678 |
| 21 | 32944292555934 |
| 22 | 138825972053046 |
[1,6,30,138,618,2730,11946,51882,224130,964134, 4133166,17668938,75355206,320734686,1362791250, 5781765582,24497330322,103673967882,438296739594, 1851231376374,7812439620678,32944292555934, 138825972053046] |