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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 2 |
| 3 | 8 |
| 4 | 18 |
| 5 | 52 |
| 6 | 152 |
| 7 | 492 |
| 8 | 1618 |
| 9 | 5408 |
| 10 | 18452 |
| 11 | 64132 |
| 12 | 225432 |
| 13 | 800048 |
| 14 | 2865228 |
| 15 | 10341208 |
| 16 | 37568338 |
| 17 | 137270956 |
| 18 | 504171584 |
| 19 | 1860277044 |
| 20 | 6892335668 |
| 21 | 25631327688 |
| 22 | 95640829924 |
| 23 | 357975249028 |
| 24 | 1343650267288 |
| 25 | 5056424257552 |
| 26 | 19073789328752 |
| 27 | 72108867620204 |
[1,2,2,8,18,52,152,492,1618,5408,18452,64132, 225432,800048,2865228,10341208,37568338,137270956, 504171584,1860277044,6892335668,25631327688, 95640829924,357975249028,1343650267288, 5056424257552,19073789328752,72108867620204] |