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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 12 |
| 5 | 31 |
| 6 | 90 |
| 7 | 264 |
| 8 | 797 |
| 9 | 2402 |
| 10 | 7355 |
| 11 | 22725 |
| 12 | 70573 |
| 13 | 220007 |
| 14 | 688379 |
| 15 | 2160568 |
| 16 | 6798020 |
| 17 | 21428295 |
| 18 | 67644503 |
| 19 | 213806475 |
| 20 | 676499166 |
| 21 | 2142338437 |
| 22 | 6789119425 |
| 23 | 21527297986 |
| 24 | 68292751071 |
| 25 | 216737768906 |
| 26 | 688082702872 |
| 27 | 2185085230180 |
| 28 | 6940609839680 |
| 29 | 22050162168754 |
[1,1,2,4,12,31,90,264,797,2402,7355,22725,70573, 220007,688379,2160568,6798020,21428295,67644503, 213806475,676499166,2142338437,6789119425, 21527297986,68292751071,216737768906,688082702872, 2185085230180,6940609839680,22050162168754] |