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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 43 |
| 5 | 163 |
| 6 | 631 |
| 7 | 2525 |
| 8 | 10321 |
| 9 | 42811 |
| 10 | 180088 |
| 11 | 765880 |
| 12 | 3286441 |
| 13 | 14215607 |
| 14 | 61902944 |
| 15 | 271139438 |
| 16 | 1193813735 |
| 17 | 5280214067 |
| 18 | 23449724862 |
| 19 | 104524431296 |
| 20 | 467440584451 |
| 21 | 2096715316321 |
| 22 | 9430597111447 |
| 23 | 42522968296897 |
| 24 | 192180053280261 |
| 25 | 870389180724247 |
| 26 | 3949764095984244 |
| 27 | 17956474896695226 |
[1,1,4,12,43,163,631,2525,10321,42811,180088, 765880,3286441,14215607,61902944,271139438, 1193813735,5280214067,23449724862,104524431296, 467440584451,2096715316321,9430597111447, 42522968296897,192180053280261,870389180724247, 3949764095984244,17956474896695226] |